Thursday, October 12, 2017

Cells Are Great Multitaskers

Biology concepts – compartmentalization, organelle function, cellular biochemistry

This chart represents a portion of the cellular reactions
that are taking place every second in a mammalian cell.
It looks more like a multicolored plate of pasta, but
shows you how complex a single cell is, and remember
that this doesn’t even count all the reactions for one cell
to be able to talk to another cell.
It is hard to estimate the number of reactions that must take place in a cell every second in order to keep a cell alive and performing its jobs(s)...... but I bet it is more than seven or eight.

The typical mammalian cell contains 2000 or more different proteins as well as many thousands of non-proteins (lipids, carbohydrates, and nucleic acids). Each molecule is crucial for carrying out chemical reactions, and each individual molecule is itself produced, modified, and destroyed by chemical reactions.

When I started to think about all this chemical activity, I looked to see if someone had counted, or at least estimated, the number of reactions taking place in the cell at any one time. I got no answer, not even a reliable guess from a credible source.

Think of it in this light, a plant cell has to perform more than twenty reactions to convert one photon of light into the chemical energy that will later be used for the synthesis of glucose. Each of these twenty reactions is occurring simultaneously at least hundreds of times in every chloroplast of the plant cell, and a single plant cell might have more than one hundred chloroplasts. The numbers add up fast, but remember that production of carbohydrate from light energy is just one of thousands of functions of a plant cell. There are chemical reactions occurring every second for all of these functions.

All this chemistry results in perhaps hundreds of thousands or millions of reactions each second, and all taking place within the confines of a cell that is too small to be seen with the naked eye. Wow!

When talking to students, I often use the analogy that a cell is like a factory, producing many different products at the same time. Not unlike a factory, a cell has to perform many functions, such as energy production, product manufacture, oversight and management, transportation of products, quality checks, and cleanup. What complicates matters is that all these different jobs have to be able to occur simultaneously.

I often use the analogy that a cell is like a factory, with
different departments. Other like the cell as a city
analogy. I even had one student make the analogy
that the cell is like a movie set, where the nucleus is
the director, and the plasma membrane is the fence
around the movie lot, etc.   She got an A.
How can a factory, or a cell for that matter, keep all the parts for all the different products, all the different workers, and all the different processes and jobs from messing each other up? A factory does this by setting up departments, where individual jobs take place, and then creating management teams that coordinate the work of the different departments—although to often there is too much management and too little production, but that is another matter.

The business and manufacturing industries stole this strategy from the cell, just as most our good ideas have been copied from nature. The cell uses compartments to increase the efficiency of all its needed chemical reactions. In eukaryotic (eu = true, and karyo= nucleus) cells, the compartments are called organelles (organ = instrument and elle = small), most of which are membrane bound containers.

Remember in our discussion of why cells must be small (It’s All In The Numbers) we said that mixing rate (time needed for a molecule to become evenly dispersed in a cell) and traffic time (time needed for two molecules needed for a certain reaction to find one another) are important for determining the maximum size of a cell.

Membrane bound organelles sequester needed components and create different local environments so that their mixing rates and traffic times are reduced. The result is a cell that is more efficient and can be bigger. This is evidenced by the fact that prokaryotic (pro = before) cells, such as bacteria, don’t have organelles and are about 50 times smaller than eukaryotic cells which have evolved organelles.

The nucleus has two membranes that form an envelope.
The outer membrane is continued as the endoplasmic
reticulum (ER), another vital cell organelle. The ribosome
attached to the ER, so it is easy to see how the organelles
work together to make a functioning cell.
The membranes of organelles look a lot like the membrane that surrounds the cell itself, but organelle membranes are often modified for their particular job. Take the nucleus (Welsh for "kernel of a nut," meaning the central part of a thing) for instance. It has two membranes and nuclear pores that run through both membranes are very specific for what they will let into and out of the nucleus.

The plasma membrane of the cell also limits the passage of molecules, but the nuclear pores are a complex of many unique proteins and this structure that is nowhere to be seen on the cell’s plasma membrane. Just like the membrane of the cell separates what is in the cell from what is outside the cell, the membrane of the organelle separates the needed components of their reactions from all the unneeded components of the cell.

In addition, many chemical reactions in organelles require the membrane as a workbench. Thousands of reactions take place in or across the membrane. This is an important function of many types of organelles, they increase the membrane surface area of a cell without making it bigger.

Some cellular reactions produce or use an intermediate molecule that must be separated across a membrane in order for the rest of the reaction to take place. This is the case for the mitochondrion – the energy producer in eukaryotic cells. To produce ATP (adenosine triphosphate, the chemical currency unit of energy in the cell), the mitochondrion sets up a gradient of protons between two membranes (remember that the nucleus has two membranes also) of the mitochondrion. The energy from the leaking of protons back into the inner space is used to produce ATP. We will talk more about these organelles with two membranes in an upcoming post.

Second messenger systems allow for messages from outside
the cell to be transmitted throughout the cell. There are three
general types, including one for gases like nitric oxide. In all,
there are more than two dozen different signal transduction
cascades, each with its own set of reactions.
Likewise, the outer membrane of the cell has many jobs that require messages to be transferred from one side of the membrane to the other. Called second messenger systems, these reactions are mechanisms to bring messages from outside the cell to the inside of the cell without the need for anything to cross the cell’s boundary.

In some cases, the membrane is not enough compartmentalization. The lysosome is an interesting organelle whose job is to break down many complexes that are brought into a cell and to recycle old organelles so the cell can reuse the parts. To do this, the lysosome contains proteins that can eat up other proteins, lipids, and carbohydrates. Unfortunately, these are the exact same molecules that make up the cell and the lysosomal membrane themselves. So why doesn’t the lysosome digest itself, and the entire cell for that matter?

The protein enzymes in the lysosome work efficiently within a narrow range of acid pH. Therefore, this organelle is acidified when produced. If the lysosome ruptures, the 7.2 pH of the cytoplasm will inactivate the lysosomal acid hydrolases, so the cell is protected. In addition, the lysosome membrane has many sugars stuck to it that act as a buffer between the lipids and proteins of the lysosomal membrane and lysosomal enzymes. There probably is some damage to the lysosome membrane, but repair reactions also help to keep the membrane intact. The cell often has redundant systems for safety.

So, we have seen that many of the organelles function to keep things sequestered in the cell, either for protection, organization, efficiency, or function. However, there are other reasons why organelles are a good idea.

Osteoclasts and osteoblasts are hard workers, so much so
that they needed more than one set of instructions for their
work. The osteoclast above shows multiple nuclei for many
DNA copies. Sometimes separate osteoblasts will join
together to form a multinucleated giant cell.
Organelles increase specificity, both for individual reactions and for cellular activity as a whole. Many cells in multicellular organisms are specialized for a certain function, and their organelles help them carry out this function. For instance, muscle cells are specialized for contraction, and this requires lots of energy. Therefore, they need many mitochondria, but few other types of organelles. These cells might contain 10-100 times more mitochondria than other cell types.

Likewise, osteoclasts (osteo = bone, clast = break) cells break down bone – and yes, you are breaking down and rebuilding your bones every second of every day. This activity requires many proteins to be produced, and one set of DNA instruction housed in one nucleus is often insufficient for the job. Therefore, these cells often have two or more nuclei in order to get the job done.  In these ways, specialization of organelle compartments and combinations allows for specialization of cellular function.

Centrioles are organelles important for the cellular
division. They are also a target for cancer therapy,
since many cancer cells have more than the regular
set of two centrioles.
As we have seen in every topic we have investigated, there are exceptions in the world of organelles. Some organelles are not membrane bound bags that carry things around or house certain reactions. Ribosomes are cellular organelles that make proteins, but they have no membrane. The cytoskeleton elements help the cell hold its structure, help the cell move, and help move other organelles move around within the cell, but they are not membrane bound either. Other cellular components, like the mitotic spindles of the centrioles that pull chromosomes apart when the cell undergoes mitosis are proteins that are present at only certain times in the animal cell. Even more confusing, plant cells divide similar to animal cells, but don’t have centriole organelles.

The take home message is that these organelles, whether membrane bound or not, perform vital services for the cell and make the many cellular reactions possible. The general modus operandi for organelles is that they carry out their functions with in the cell, but one type of organelle is the exception, it’s the traveling organelle.

Song RL, Liu XZ, Zhu JQ, Zhang JM, Gao Q, Zhao HY, Sheng AZ, Yuan Y, Gu JH, Zou H, Wang QC, & Liu ZP (2014). New roles of filopodia and podosomes in the differentiation and fusion process of osteoclasts. Genetics and molecular research : GMR, 13 (3), 4776-87 PMID: 25062413

Saltman LH, Javed A, Ribadeneyra J, Hussain S, Young DW, Osdoby P, Amcheslavsky A, van Wijnen AJ, Stein JL, Stein GS, Lian JB, & Bar-Shavit Z (2005). Organization of transcriptional regulatory machinery in osteoclast nuclei: compartmentalization of Runx1. Journal of cellular physiology, 204 (3), 871-80 PMID: 15828028


For more information on organelles, see:

Organelles –

Thursday, October 5, 2017

More Than The Sum Of Its Parts

Biology concepts – symbiosis, lichen products, weathering, pedogenesis

During the Depression, the Civilian Conservation
Corps got the idea to have unemployed people earn
some money by planting kudzu vine in the South to
reduce erosion. It seemed like a good idea at the
time, but in biology, not all good ideas stay good
ideas. Yes, there is a cabin under all that vine.
Will today’s good idea be tomorrow’s bust? In nature, an adaptation may provide an advantage today, yet be the cause of extinction tomorrow. Conditions rarely remain the same and never duplicate themselves. Very few organisms could develop identically at different times and places – but lichens are the exception.

Genetic studies of lichens from different places and of different ages show us that these amazing organisms have developed numerous times. This doesn’t mean that different lichens have appeared and gone extinct, only to make a comeback. It means that at least seven times in the history of life on Earth, a fungus and a photobiont (algae or cyanobacteria) have developed the exact same symbiotic relationship that we see in today's lichens.

Each of these original ideas has used different fungus types and sometimes different photobionts, but their relationship is identical in each case. Think of that, lichens are such a good idea that over 4 billion years, in deserts, forests, and coastlines lichens have invented themselves again and again. That must be one good idea!

One reason lichens have been so exceptional is that they can survive in places that can’t support much life. This may be the link in the separate development of lichens time and time again. One reason for their success in desolate environments is that they are veritable chemical factories. They make many products, some of which have uses in their stark homelands. Many of these products are unique to lichens.

Lichen acids (also called lichen substances or lichen products) are chemicals made by the lichen by further processing of regular cellular products, making them secondary metabolites. Lichens make 600-800 of these products, and all but 60-80 of them are unique to lichens.

The lichens themselves can be different colors, based on their
constituents. However, their colors may be hidden under the
different lichen products excreted from the cortex onto the thallus.
Here the lichen products are white and crystalline, and probably
mean that the conditions aren’t great for lichen growth.
Even more amazing, neither the fungus nor the algae (or cyanobacteria) that make up the lichen produce lichen acids when they are on their own. Many are made by the fungal component of the lichen, but the type of photobiont included in the symbiosis will control which lichen acids can be made. Most are produced as crystalline powders that are deposited extracellularly, on the stalks or the thallus bodies.

Making lichen acids would be wasted energy if they did not confer some advantage to the lichen, and evidence suggests that they do have specific functions. Lichens that are growing rapidly (for them, still might be only 1 mm/year) make very little of these lichen products. When exerting energy to make biomass, the lichen doesn’t need the lichen acids. This suggests that the acids are most needed when the going is tough, when lichens are trying to survive in poor conditions, ie. on difficult substrates, in drought, in extreme temperature or radiation, etc.

What is more, there must be very specific functions for the different acids based on what the lichen needs to do to survive. Lichens of identical morphology and made up of the same component fungus and algae can make very different acids, depending on their location or environment. Lichens can be grouped into complexes of similar organisms, but they may make different lichen acids.

For example, the Ramalina siliquosa complex of lichens is found on the Atlantic coastline of Europe. Low on the cliffs, most exposed to the sun and saltwater, R. cuspidate produces a lichen acid called stictic acid. However, high on the cliffs, away from the wind and facing toward the continent, R. crassa produces lots of hypoprotocetraric acids, but no stictic acid at all. Finally, R. stenoclada lives in the region between the other lichens, and produces a different lichen acid, norstictic acid. These different positions must present different growth challenges, and the lichens respond by making different acids.

So what do these lichen products do for the symbiots? They can dissolve rock to help anchor the lichen, and they can increase membrane permeability to permit flow of carbohydrates from the photobiont to the mycobiont. Many functions have been proposed and demonstrated, and one lichen acid, usnic acid, is a particularly good example of many of these functions.

Usnic acid is a dye that provides many advantages to the lichen,
but has also been a traditional dye for yarn for hundreds of years.
Usnic acid was first described in 1844, and is a yellow-green dye. Its color provides protection for the lichen from damage by visible and UV light, but this is just the beginning. Usnic acid is also important for protection of the lichen from predation. It has anti-herbivore properties, meaning that tastes bad or is toxic to the snails that like to make a meal of lichens. It has the same effect on insects and many fungi and microbes.

Antibacterial properties are particular strong for usnic acid. Many lichen acids are effective against a group of bacteria called Gram+. These include Mycobacterium tuberculae, several streptococci and staphylococci and some pnemuococcus. But a 2011 study indicates that usnic acid can go even further, and is toxic to Helicobacter pylori, the organism responsible for causing many stomach ulcers. Importantly, the usnic acid is not toxic to the photobiont component, whether it be cyanobacteria or algae. In addition, usnic acid has demonstrated anti-inflammatory properties and is a painkiller (analgesic).

But the most promising and surprising activity of lichen acids is as a degrader of prion proteins. Misfolded prion proteins are lethal to humans and other organisms (see -An Infectious Genetic Disease) and are resistant to being broken down by all known human protease enzymes. But a few lichens can produce a protease that destroys prions, some down to the level of undetectability.  Fungi themselves are susceptible to prion diseases, so this may be why the lichens produce anti-prion enzymes, but no one has checked lichens for prions. Not enough is known yet to predict if lichen products could be used as treatments for Creutzfeld-Jakob or fatal familial insomnia; here’s your chance to win a Nobel Prize!

This may be an important human use for lichens, but humans have been using lichens for thousands of years. Many of the dyes we use are lichen acid based, as is the litmus dye used in pH paper. Other uses have been more inventive, like as stuffing in Egyptian mummies and in Native American Indian diapers! If these don’t appeal to you, perhaps the Iceland-made lichen schnapps will be more your style. It supposedly tastes a lot like mouthwash.

However, we are amateurs compared to lichens in using the lichen acids. Lichens also use these products to grown on rocks. No soil needed. Crustose lichens are firmly attached to rock surfaces; they can’t be separated without damage…. to the rock.

Some lichens can protect themselves from poor environments by
Living within the rocks. Euendolithic lichens, like the one shown
above, bore into the rock using lichen acids, and then grow under
the surface of the rock. “You make a better door than a window,”
apparently doesn’t apply to rocks, because the endolithic lichens still
get enough light to perform photosynthesis.
Lichen acids can chemically weather rock by literally dissolving it. This provides crevices for the lichen to attach itself. Lichens can live on top of the rock (epilithic, epi = on top, and lith = stone), or they can be endolithic (within the stone). Within endolithic types, they can be chasmolithic, meaning they limit themselves to the fissures in the rocks and between the mineral grains, or they may be cryptoendolithic, meaning that the lichens grow within natural cavities in the rock. Finally, there is euendolithic lichens, and these are the toughest guys. They can dissolve the rock to the point of boring directly into the rock and creating its own cavities. Interestingly, the lichen will absorb much of the dissolved minerals, up to concentrations that would kill other organisms. This may prevent predation by making the lichen toxic to things that might eat it.

This ability to grow below the surface of a rock is exceptional. The photobiont must still be close enough to the surface to receive sunlight, but growing beneath the surface can protect the lichen from destructive forces of nature. Together with lichen acid protection from UV radiation and the lichens ability to survive extreme temperatures, the ability to grown inside rocks has implications for space travel. 

We know that lichens can survive in space (I’m Likin’ The Lichen) and growing inside rocks would protect them from re-entry temperatures, so could lichens have arrived on Earth from outer space? Pangenesis is the theory that life on Earth arriving from other planets, and lichens seem like a natural for this process. Unfortunately, pangenesis is most often considered with bacteria alone, and as a theory it has not got much to support it. But it is still an interesting proposition.

This rock is getting a good does of biological weathering. Tree roots,
lichens, and probably burrowing animals are all working to reduce
this noble boulder to gravel.
Growing inside rocks and dissolving the rock as needed promotes weathering breaking down of rock). Two type of weathering are brought about by lichen grown. Physical weathering comes primarily from turgor pressure. When the lichen takes up water (when it can get some), it swells and puts pressure on the fissures of the rock. Over time, this will lead to cracks and parts of the rock falling off.

There is also chemical weathering. This comes from the lichen acids dissolving the rock. Some of the minerals are mixed with the bits of rock that break off due to physical weathering and the organic material left over from dead lichens. All together, this makes soil. The process of pedogenesis (soil formation) is an important aspect of lichen growth. Making soil promotes the succession of bigger and more complex life forms, which then continue the weathering and soil formation. Look around you, all that dirt outside your window, deeper than you could dig, is there because of lichens started it all off – amazing. Lichens could be the most important player when it comes to human terraforming (terra = Earth and form = make like) another planet for future colonization.

Lichen growth on Easter Island. This ancient
statues can’t survive much Moai!
Not everything about weathering rock by lichens is good; consider their effects on stone statues. Some people say that the covering is protective, keeping the wind and sun from damaging the statue, but other say the chemical weathering promotes their breakdown. At Mount Rushmore, workers actively scrub the mountain to remove lichens and prevent the aging of Presidents Lincoln, Roosevelt, Jefferson, and Truman. How would you like to have that job, hanging off a cliff scrubbing out Theodore Roosevelt’s huge nostrils?

There is a strange dichotomy with lichens. They have arisen many times. They live thousands of years. They live in space, surviving radiation, extreme temperatures, and dryness. But lichens are very susceptible to pollution, it kills them or stops their growth.  Lichens have billions of years of success behind them, but it took humans to find a way to kill them off. As such, we now use lichens as indicator species, to determine if pollution concentrations are affecting nature. They built our world, now maybe they can help us to save it.

Heng Luo, Yoshikazu Yamamoto, Hae-Sook Jeon, Yan Peng Liu, Jae Sung Jung, Young Jin Koh and Jae-Seoun Hur (2011). Production of Anti-Helicobacter pylori metabolite by the lichen-Forming fungus Nephromopsis pallescens Journal of Microiology DOI: 10.1007/s12275-011-0289-9

For more information on lichen products, biological weathering, or pedogenesis, see:

Lichen acids –

Biological weathering –

Pedogenesis –

Thursday, September 28, 2017

I’m Likin’ The Lichen

Biology Concepts – symbiosis, mutualism, lichens

The lycan is a subject better relegated a cryptozoology
blog. Along with the Loch Ness Monster, vampires, and
the Easter Bunny, cryptids are those animals for
whom there is little or no solid evidence, yet the search
for them by some devotees continues.
A current movie craze has been to replace werewolves with lycans, animals that can control there physical changes to wolf, and can survive under difficult conditions. I know of another organism that has even greater powers, but wouldn’t make a great movie monster – they don’t move and are very slow growing.

Lichens (not lycans) are some of the most intriguing species on Earth, and may very well be the most amazing organisms off Earth as well. Lichens don’t necessarily break a lot of biological rules; they just refuse to acknowledge that our rules apply to them. They write their own rulebook, and humans can’t come close to playing by their rules. They make us look like such wimps. In lichen gym class, we wouldn’t be picked last - we wouldn’t picked at all.

Lichens are symbiots of two completely unrelated organisms; one is the mycobiont, which is always a fungus. The other component is the photobiont, and can be either a green algae or a cyanobacteria. The fungal partner of the lichen makes up about 80% of the mass, but the algae or bacterial component is photosynthetic. Therefore, when they become a mutualistic symbiot, the mycobiont provides a structure and a foothold to a surface, while the photobiont supplies energy through photosynthesis.

Lichens provide food for many animals. For instance, the
Cladina Stellaris grows in the desolate Arctic. It provides
food for the resident reindeer, who we know from past posts
can disconnect its biological clock and feed all through the
day. The reindeer must be particular though, because it will
take the reindeer lichen decades to recover from grazing,
since it grows only 3-5 mm each year.
This is the first exception when dealing with lichens – what are they? They certainly aren’t plants, since they contain a fungal element and not plant element. But they aren’t fungi, since they also contain a bacterial (the cyanobacteria) or protist element (the algae). They are kings in search of a kingdom. Just like Lady Gaga, they defy classification as normal life!

Fungi are decomposers; they break down organic materials to produce nutrients and carbohydrates. But in the lichen, the photobiont produces glucose by photosynthesis, so there is no need for the fungi to decompose for energy. The lichen stores most of its soluble carbohydrate as sugar alcohols, which are made by the fungal component from the algae/cyanobacteria-produced glucose. Therefore, the fungus provides a carbohydrate storage mechanism as well as a structure. These aspects give lichens the ability to live where neither the fungus nor the algae could live on its own.

The second amazing aspect of the lichen symbiosis is that the lichen doesn’t look like either the fungus or the algae that makes it up. It also doesn’t look like a mix of the two. The lichen creates a whole new morphology, with the photobiont housed below a layer of the modified fungus. In the case of lichens, you add 2 + 2 and get a Chevy.

The thallus is the body of the lichen (latin for “green shoot”). In most cases, the thallus is a layer of the fungus, called a cortex, with the photobiont house just below the cortical layer. Enough light still reaches the algae or cyanobacteria in order to make photosynthesis possible.  Below the photobiont layer is the medulla, and can include a stringy (hyphal) fungus layer or maybe just the gelatinous photobiont. Finally, some lichens will have a lower cortex layer of fungus as well. The take home message is that neither the fungus nor the algae or cyanobacteria take on any of these forms UNLESS they are part of a lichen – it is a completely different structure.

Not every lichen has a lower cortex layer, but almost all
have the top cortical layer of tough fungal material. This
layer protects the lichen from predation and dessication
(it does nether spectacularly well). The photobiont lives
primarily in the subcortical symbiont layer, while the
medulla is spongy and has many fungal filaments. The
rhizine connects the lichen to its substrate, but many
lichens are erhizinate, they do not have rhizines.
The mycobiont is the more flexible of the two components; literally thousands of different fungi can act as the mycobiont. On the other hand, only 100 or so different photobionts exist. Most common of these are of the species Trebouxia. They are green algae which rarely live on their own, they have become specialized for symbiotic life as a lichen.

The combination of these two components yields the over 17,000 different lichens that have been identified. The combinations are also flexible, a lichen may use different photobionts during its life, and identical lichen types may use different photobionts even within the same general area.

The combinations of decomposer and autotroph that make up lichens are hearty and diverse. Fully 8% of the Earth’s surface is covered with lichens, not bad for something so small. More amazing is that lichens can survive in places that support almost no other life. Lichens and endolithic bacteria are only living things in the McMurdo Dry Valleys of Antarctica, as well as the Atacama desert of Chile, often called the two driest places on Earth (I think they forgot about Lynchburg, TN).

The McMurdo Valleys (4,800 sq. km) are a cold desert environment (Water, Water, Everywhere). They are almost ice and snow free, even though they are on the frozen continent of Antarctica. Less than 200 mm (8 in) of precipitation is available each year, and most of this is from summer glacier melt.

The Atacama Desert in Chile is a desolate wasteland,
no offense to any inhabitants. It probably has its
nice parts too.  Parts of the desert have had no
recorded rainfall..... ever. This leads to some
interesting formations, like these geometric salt
patterns, very appropriate for this series of posts.
The average rainfall in the entire Atacama Desert is even less, only about 1mm (0.04 in) per year, and many weather stations have never recorded any precipitation at all. The lichens survive on the water vapor that reaches them from the coastal fog,which comes from 150 km (80 miles) and a mountain range away. Interestingly, an extreme Antarctic cold front brought 80 cm (31.5 in) of snow to the plateau in July of 2011! This was enough to bring wildflowers to the Atacama, in places they had never been seen before.

Despite (or perhaps because of) these arid environments, lichens are the major form of life in the Atacama Desert and McMurdo Valleys. Most organisms cannot survive a loss of 20% moisture, but lichens can do just fine when 90% dehydrated. While their growth may be retarded, they quickly make up for it by absorbing up to 35x their mass in water when it is available. Lichens dry out slowly because of the dense cortex of fungus on the outside, so they can still photosynthesize despite long arid periods.

Even more exceptional, the lichen symbiot is less than 50% water, even on a good day. Mushrooms are 92% water, and algae or bacteria are typically 96% water, but when you put them together as a lichen, their normal water content is some 40-45% lower. This is how the lichen can live in places that would not support either of its components on their own – amazing.

The deserts, both cold and hot, allow the lichens to show off another of their skills. Lichens can withstand extreme temperatures and wild swings in temperature. Scientists keep thinking up new ways to torture them. Lichens survived a bath in liquid nitrogen at -195 ˚C. Not satisfied that they had been treated harshly enough, European Space Agency scientists strapped some lichens to a rocket and exposed them to the cold and radiation of outer space for 14.6 days. Cold, hot (shielded re-entry), vacuum, UV, cosmic rays – the lichens survived just fine. Because of this will to live, exobiologists (scientists who study what life on other planets might be like) study lichens as a model alien life form or as an organism with which we might seed other planets.

Lichens (or something similar to them) are likely to be found on other planets, but they also may affect other forms of life off Earth. A recent study by performed in Italy and the UK has shown that the few animal types (rotifers, nematodes) that are able to survive dessication as lichens can are influenced greatly by their environment. They may have different ways to survive drought, but statistical modeling shows that the type of lichen they are found in has more to do with their survival in drought or even in space than their own tolerance mechanisms.

Lichenometry is the art and science of investigating
how long a surface has been exposed. For example,
moraines are gatherings of stones at the edges of
glaciers. How long has it been since the glacier receded
from that spot? Lichens grow at a predictable rate given
a known environment, so measuring the size of a lichen
will give good estimate of how long the surface has been
available to be lichenized (just made up that word).
As a result of the poor environments where lichens can be found (although they also grow just fine in temperate areas- just look outside your front door), lichens are the slowest growing life forms on Earth. Usnea sphacelata, which looks like a small forest of bonsai, grows about 0.01-1 mm per year. Usnea can only grow on about 120 days per year, but they live a very long time. An age of 200 years is not unusual, the record is about 4500 years.

In a defined area with a defined weather pattern, lichens may grow at a very slow rate, but it is a very consistent rate. This predictability makes them good for dating other structures, a process called lichenometry. For instance, lichens can be use to estimate how long a rock face has been exposed by a retreating glacier. Once the rock is uncovered, lichens will soon colonize it and grow at a consistent rate. Once you know the size of the lichen, identify the type of lichen, and know its growth rate for that area, an age for the exposure can be calculated.

Next week we will talk more about the amazing properties and abilities of lichens, but one last tidbit for today. For anyone who has read Peter Rabbit or Benjamin Bunny to their child, Beatrix Potter is a familiar name. Before becoming a famous author, Beatrix made a living by illustrating other author’s books and doing some scientific illustrations. She was an outdoorsy girl, and her pictures of lichens led her to study them on her own.

Beatrix Potter wrote more than 20 childrens classics; the
illustrations were her own and are perhaps more iconic than
her prose. But she started out working on lichens, and was a
devout “Schwendenerist,” a follower of Simon Schwendener’s
idea of lichen symbiosis. I got the chance to collaborate with
one of Simon’s distant relatives a few years ago. Hi Reto!
While the dual hypothesis of lichens had already been put forth by Simon Schwendener, it was not well received in England. Potter used microscopy and her drawings to generate evidence for Schwendener’s hypothesis. However, she was not a scientist, and worse, she was a woman – so she couldn't present her evidence to the botanists of her time. Her uncle was Sir Henry Roscoe, the eminent scientist who developed the first flashbulbs for photography (along with another scientist named Bunsen – name sound familiar?). He supported her and read her papers into the scientific record, but she could never make name for herself as a scientist in that environment, so she turned to writing. It was a lucky thing for us all – a world without Flopsy and Mopsy is too horrible to imagine.

Fontaneto, D., Bunnefeld, N., & Westberg, M. (2012). Long-Term Survival of Microscopic Animals Under Desiccation Is Not So Long Astrobiology, 12 (9), 863-869 DOI: 10.1089/ast.2012.0828
For more information or classroom activities on lichens, exobiology, or lichenometry, see:

Lichens -

Exobiology –

Lichenometry –

Thursday, September 21, 2017

Water, Water Everywhere, But….

Biology concepts – symbiosis, mutualism, water storage

“Gobi” means desert in Ural-Altaic,
so when you say, “Gobi Desert,” you
are really being redundant.
Sometimes the places with the most water are the most lifeless areas. Everyone thinks of sand and heat, but Lawrence of Arabia wouldn’t even recognize most biological deserts.

The term biological desert is misleading, since places like the Gobi Desert in Asia support over 600 species of plants and hundreds of animal species, vertebrate and invertebrate. Death Valley in the USA has over 100 plants species; it could hardly be called dead! A biological desert has less to do with the climate and more to do with the adaptability of organisms to adverse conditions of oxygen, salt, water, light, or too often - pollution.

Take for instance the South Pacific Gyre. This area of about 34 million square kilometers (10 million sq. miles) has very little life in the pelagic zone (the below the surface waters to just above the sea floor). In the last posts we learned why water and salts are crucial for life, and the extreme evolutionary adaptations that have occurred in many organisms in order to conserve body water and maintain safe salt levels. But here we are in the ocean – water everywhere, salt everywhere, but almost nothing lives in the gyre.

The north and south Pacific gyres represent
a huge portion of the Earth’s surface, and
these are relatively life free areas, the largest
deserts on Earth.
The reason for this paucity of life has more to do with nutrients than with water or salt. Because the current moves counter-clockwise, the center of the gyre is isolated from the upwelling of nutrients from the ocean floor, and the winds can’t help to churn the waters. Even if they could, it would help little. The waters of the gyre are rigidly layered due to salt and temperature differences (stratification, I Am Your Density), so nutrients find it difficult to travel to the surface from below. Adding to the problem, there is little landmass in the South Pacific, so windblown organic material and terrestrial runoff are limited. Nutrients are coming from neither above nor from below.

With limited nutrients, there is a ceiling to the amount of primary productivity of phytoplankton (phyto = plant, and planktos = wandering in Greek) that can take place. Fewer producers means that few primary consumers can be supported, and so forth up the food chain. Little life on the surface means few nutrients drop to the ocean floor (waste and dead organisms), and so on.

The ocean gyres have little upwelling if nutrients
and therefore little plankton production. The bad
news - with global climate change, the gyre-related
low productivity zones are growing in size.
Strangely enough, the lack of producers in the gyre has benefited humans in at least one aspect. The chlorophyll of the producers changes the color of the ocean, and this affects the trapping of heat and the wind currents. With a loss of living things in the North pacific gyre, a 2010 study states that typhoon formation has decreased in this region by more than 70%............Don’t get too excited, global surveying also says that the biological deserts of the gyres are growing much faster than global warming models would predict. As they grow, global productivity will be reduced, and that can’t be good for any of us.

We don’t make things any easier by letting chemicals run into the oceans either. Man made dead zones from increased nitrogen and phosphorous. These nutrients are needed for growing phytoplankton, but you can have too much of a good thing. The overgrowth of phytoplankton and algae in these areas, along with the decomposers they support, deplete O2. The result is that there is no oxygen left for succession organisms, so larger animals cannot live there (neither can the plankton or algae after a while).

Man made dead zones correspond to areas of
runoff from sprayed fields. For instance, the estuary
of the Mississippi River in the Gulf of Mexico forms
the second largest man made dead zone in the world
each summer. Not to be outdone, the Baltic Sea dead
zone in Northern Europe is the largest, and it is
present all year round.
So the gyres are “almost dead” zones, and some polluted estuaries are considered dead zones. What about a body of water with dead in its name, the Dead Sea? At 423 meters (1388 feet) below sea level, the Dead Sea is officially the lowest body of water on Earth. Water flows into it, but not out of it, so all the salts and minerals just accumulate.

The temperature of the desert surrounding the Dead Sea is warm enough that evaporation plays a factor in increasing the salinity and mineral content of the remaining water. Only certain types of bacteria and algae can survive in the 33.7% saline waters (~8.6 x the salinity of the Mediterranean Sea).

 Dunaliella salina algae are particularly abundant in the Dead Sea after the rainy season. These green algae produce antioxidant carotenoids to protect themselves from the intense sun exposure of the Jordan Rift Valley as well as huge amounts of glycerol (a three carbon carbohydrate) to counteract the osmotic pressure which would otherwise move all the freshwater out of the algal cells.

The algae is a good food source for halophilic (salt-loving) bacteria. However, during dry years, both the alga and bacteria are present in much lower numbers. But isn’t just the high salt that prevents larger plants and animals from living in the Dead Sea. The minerals that accumulate, such as magnesium chloride, calcium chloride, magnesium bromide, and calcium sulfate, are toxic to animals that drink the water. Fish from the freshwater feeders of the Dead Sea sometimes swim into the mineral-laden waters and are killed almost instantly.

The Dead Sea has receded a mile in the past twenty
years, and environmentalists warn it could be
completely gone by 2050. As it recedes, it leaves
salt on the rocks after the water evaporates.
The exception to this is the recently discovered freshwater springs that also feed the Dead Sea. Along the sea bottom near these vents lives a multitude of Archaea (often called extremophiles) that used to be classified as bacteria, but are now known to be a different kingdom of life. Spreading along the seafloor, mats of Archaea form biofilms, previously unknown in the Dead Sea.

The Great Salt Lake in Utah is similar to the Dead Sea biologically, but the lower salinity (some places are 5% salt, while others are 25 %; a railroad causeway has separated it into a more saline north arm and less saline south arm) allows more types of organisms to thrive in the water. Still no fish, but more types of algae, as well as some brine shrimp and brine flies.

Surprisingly, there is abundant flora and fauna around both the Great Salt Lake and the Dead Sea. The Jordan Rift Valley boasts camels, leopards, and ibexes, as well as fig trees and the rose of Jericho. In the western hemisphere, the Great Salt Lake has millions of shore birds, mostly fed by the 100 billion brine flies that hatch each summer. It is just the exception that here you have to move away from the water to find the life.

The above two examples indicate areas that have a lot of water, but too much salt for it to be useful. There is another place on Earth that has plenty of H2O, but not enough liquid water to support much life – does that make sense?

Antarctica. It is hard to believe that with all that ice, miles thick in some places, there is not enough free water to keep plants and animals alive, but in many parts of the continent, that is the case.

McMurdo Station is the largest community on
Antarctica, if you don’t count the penguins. It is
located near the McMurdo Dry  Valleys, the driest
places on Earth. This is due to the katabatic winds.
Cold air is more dense, and is pulled downhill. The
wind can reach speeds of 200 mph, and as it warms,
it evaporates all the moisture on the ground and in the air.
Some areas of Antarctica do support a little life; two vascular plants exist on the frozen continent, hair grass (Deschampsia antarctica) and the pearlwort (Colobanthus quitensis). These plants only grow on the west coast peninsula.

In the McMurdo Dry Valleys, east of McMurdo Station and the Ross ice sheet, almost nothing grows. There are hypersaline lakes here that put the Dead Sea to shame, including the Don Juan Pond that is 18x the salinity of the ocean.  

There are no vertebrate animals in the valleys; microbes make up all the biology there. In all of Antarctica, only 67 species of insect are found, and most of these live as parasites on penguins.

The exception is the wingless midge (Belgica antarctica). At an average of 6 mm long, this fly is the largest purely terrestrial and year-round animal on the entire continent (penguins only live on the continent for part of the year).  This flightless fly relative lives in algae mats, on rocks, and in the mud… just about anywhere it wants to. There are no competitors on Antarctica; this walking fly reigns supreme!

Belagica is well adapted to life in Antarctica. It is
black to absorb heat, and it is wingless so it won’t
be blown out to sea by the strong winds. It has a
short egg laying time and adult life span so that it
can complete its life cycle in the highly variable
summer season.
Other adaptations allow B. antarctica to thrive in this harsh environment. While the vast majority of plants and animals die with a relatively low level of dehydration (5-25%), these midges can survive a 70% water loss event - I suspect they can’t expectorate! In the winter…… WINTER? Isn’t it always winter there? Well, no; there is a colder season....the midge can react to winter by dehydrating and then coming back to life in the spring.  Something like having a piece of beef jerky moo after you start salivating on it. Amazing.

Recent evidence shows just how adapted B. antarctica is for the dehydration. The midge has one genetic response to thermal stress, whether it be hot or cold. They turn off some pathways and increase glucose metabolism pathways.

But in dehydration, it has different responses to different patterns of dessication. If it is a rapid dehydration, glucose metabolism pathways are up regulated, but if it is slow and steady, a whole different set of pathways are upregulated, including those for different osmoprotectant molecules (trehelose and proline).

The dry valley temperatures (-10˚C to -51˚C) could easily cause havoc with the midge’s protein function, including the pathways that protect it from dehydration stress. Heat shock proteins help to stabilize protein function in temperature extremes, usually they are expressed (transcribed from DNA and translated from mRNA) for short periods of time, only when there is an abnormal event. But Belgica’s heat shock proteins are expressed all the time. This is a huge energy investment, and an investment that few animals are willing to make. But in areas with too much salt or too little water, sacrifices must be made.

Next time we will talk about one of the greatest exceptions in biology, an organism that can live in the Atacama Desert, the Jordan Rift Valley, the Great Salt Lake, and even at Antarctica. It's not a bacteria, not a fungus, not a plant, not an animal – this is one heck of an exception.

Teets NM, Kawarasaki Y, Lee RE Jr, Denlinger DL. (2012). Expression of genes involved in energy mobilization and osmoprotectant synthesis during thermal and dehydration stress in the Antarctic midge, Belgica antarctica. J Comp Physiol B DOI: 10.1007/s00360-012-0707-2  

For more information or classroom activities on biological deserts, life in the Dead Sea, and life on Antarctica, see:

Biological deserts and gyres –

Life around the Dead Sea –

Life in Antarctica -