by Richard L. Howey, Wyoming, USA
WHAT!–moderate extremophiles–that sounds very much like an oxymoron. Almost everyone likes a good oxymoron and some of the most popular are:
So what do I mean here by “moderate extremophiles”? I want to draw your attention to the fact that we are surrounded by organisms that live in remarkable conditions which would involve the employment of extreme means for us to survive them. In fact, we humans, were it not for our technologies, would have a very narrow range of conditions under which we could survive and thrive. We are severely limited by temperature, moisture, atmosphere, and access to food and potable water. Yet all around us are organisms which have adapted in remarkable ways to conditions which would be life-threatening to us. Now that we are moving away from winter, I want to think a bit about some of the organisms that we will encounter when we begin going into the lakes, ponds, woods, and mountains. One doesn’t need expensive submersibles or snow-cats to go to the Arctic or the Antarctic to get samples from Lake Vostok below the ice shelf, nor climbing gear to descend into a crater of a volcano, nor an air-conditioned survival suit for the Sahara. We can find extremophiles in much more accessible environments.
Well, spring will soon be upon us. I think that here in the high altitude of Laramie, it is predicted for June 17th and June 18th this year. Everyone here agrees that we’ve had a very long winter. Spring, early summer, and late fall are exciting times to probe the ponds, rivers, and lakes for micro-organisms and to observe the changes in the populations as the seasons and conditions change. This year the snow pack in the mountains has been higher than normal and so the melt off, if it’s not too rapid, may produce some wonderful displays of micro-life. A significant runoff can create temporary ponds which may have been dry for several years and this influx may revive creatures that have been in limbo for a considerable period. I know of 2 places along one road which runs southwest from Laramie, where such ponds can briefly produce enormous numbers of tadpole shrimp and fairy shrimp. Their eggs have lain dormant for years and now they hatch and feed prodigiously and reproduce at an astonishing rate to produce offspring and eggs for a future time. These ponds may last only a few weeks and then return to dusty layers of cracked, dried mud. This is another example of the tenacity of life and its ability to adapt, survive, and even thrive in extreme environments. One doesn’t have to have access to deep-sea submersibles to discover these extraordinary phenomena of adaptability and tenacity; examples are all around us and, if we pay proper attention, we can discover amazing things.
The tadpole shrimp is a strange little creature which looks rather like a miniature horseshoe crab. I’ll show you 2 views. This specimen is slightly over 2 inches long.
Fairy shrimp can sometimes be found in the same temporary ponds as the tadpole shrimp (see Google Images). They, however, are much more elegant and appear deceptively delicate.
They also reproduce rapidly and produce highly resistant eggs. I have found them in tiny rock pools on cliffs and the pools may contain only 2 or 3 gallons of water, so they will not last long. These lovely creatures perform an underwater ballet and spend much time swimming about upside down. Their appendages are modified into miniature paddles which are utilized for both swimming and creating currents for feeding.
Tadpole shrimp, fairy shrimp, and clam shrimp are crustaceans which are usually grouped together in the division Eubranchiopoda and this intriguing group of odd little creatures deserves much more study.
When the ice has melted, all kinds of wonderfully fascinating and puzzling micro-creatures begin to appear: protozoa, algae, micro- and macro invertebrates.
Since we started with some of the larger forms, let’s descend gradually to more intermediate organisms in terms of size and then to the truly microscopic ones.
Let’s begin with copepods, cladocerans, and ostracods. Here, in one of the high mountain lakes, I have found a remarkable copepod–a burgundy-colored cyclops which is 2 or 3 times the size of most other cyclops which I find in the area. The lake in which it lives and thrives in the spring is, at that time of the year, extremely cold, yet here life is abundant. Quite some years ago, a couple of students I knew wanted to go along with me on my trip and they were avid scuba divers. They took their gear along and wore wet suits to stave off the cold. However, in a matter of a few minutes, they were out again unable to endure the near freezing temperatures.
Also, in one of those high lakes, one can find a wide variety of rhabdocoel worms which seem to especially like the environment created by the abundant sphagnum moss.
This environment also attracts many rotifers and tardigrades both of which are known for some remarkable survival skills. Rotifers can form resistant casings around their bodies and also lay temperature- and drought-resistant eggs which some investigators claim can last for many years until suitable conditions are restored. Tardigrades also have extraordinary resistance. You can find out more about tardigrades in the excellent article of our editor Dave Walker.
Think of the extraordinary machinations which we humans have to go through in order to achieve brief periods of “suspended animation” which still allows for resuscitation.
Here, in the early spring in the mountains, one can find “pink or watermelon snow” (also known as red snow or blood snow) ; it is an alga which is cryophilic and grows on the surface of snow banks extending down as much as 10 inches below the surface during blooms. It does indeed have the odor and taste of watermelon, but it is not advisable to do more than sample it and spit it out. It is, odd as it may seem, a green alga, Chlamydomonas nivalis, which also possesses a deep red carotenoid pigment which protects the chloroplasts from intense heat and ultraviolet radiation characteristic of high altitudes. As if finding one extremophile here weren’t bizarre enough there are others, such as, springtails or snowfleas (Achorutes nivicolus) which can occur in such number as to create miniature brown clouds and they feed on Chlamydomonas nivalis. However, it gets even more mind-boggling because ciliated protozoa, nematodes, rotifers, and a very odd creature called an ice worm (Mesenchytraeus solifugus) have also been found to feed on C. nivalis. So, just go up to a snowy mountain at 10,000 to 12,000 feet and you may get lucky and find an entire community of cryophilic extremophiles. An interesting historical footnote is the fact that Aristotle was the first to describe pink snow!
There is a respect in which we can be like nature (or play God, if you’re religiously inclined) and create extreme environments in the laboratory and see what organisms will survive. In many instances, this happens by accident as a consequence of our neglect of cultures and samples. For example, if you have a rich culture of Stentor coeruleus and you forget about checking it for days or weeks, you may discover on your return to it that some of the organisms have indeed survived, but in hardly recognizable forms were it not for the distinctive pigment. The gradual buildup of toxic waste from the organisms in the culture can precipitate the development of monster formations. However, in this instance, the organisms certainly don’t thrive and won’t survive for very long. However, there are bacteria which are very good at adapting to radical environmental changes and can not only adjust, but thrive under the new circumstances. Scientists have subjected micro-organisms to extreme treatments of many different sorts using toxic chemicals or raising or lowering the temperature or decreasing or increasing the oxygen levels or altering the pH. Some of these processes take place in nature without any interjection from humans. For example, here in the high plains there are small lakes and ponds which over the summer lose significant amounts of water through evaporation and during dry spells that water is not replaced. As a consequence, due to heavy concentrations of soil minerals, salt deposits begin to appear around the shorelines and as the summer continues, the deposits become more extensive and thicker which means that the remaining water increases very significantly in alkalinity. By late summer, the variety of organisms decreases dramatically and I have taken samples in which I found almost exclusively bdelloid rotifers and hypotrichs. I am not including bacteria which remain abundant as food. I’ll show you an example of such a rotifer and then 3 types of hypotrichs.
One of the reasons that extremophiles have such an interest for us is we think that such organisms might provide clues to what we might encounter by way of extra-terrestrial life forms and also reveal to us what sorts of strategies terrestrial organisms have developed to survive in specific conditions. As a consequence most of this research has centered on so-called primitive organisms, such as bacteria, viruses, algae, and fungi. However, after the discovery of deep sea volcanic funes or “black smokers” the notion of conditions for life have undergone a radical transformation. Giant tube worms, large red clams, crabs, and a variety of other complex organisms have been described and documented in these extraordinary places where no sunlight penetrates–thus no photosynthesis–and where there is enormous pressure. The question of metabolism was resolved relatively quickly when it was discovered that these organisms possess symbiotic sulfur bacteria which can make up about half of their mass. These bacteria can metabolize hydrogen sulfide and in this process of chemosynthesis oxygen dissolved in the water is involved. Thus indirectly these incredibly alien organisms are also dependent upon the process of photosynthesis. Here is an environment which is, from our point of view, incredibly toxic and yet we find life not only surviving but thriving there.
However, if no oxygen were available at all, nature still has strategies. There are anaerobic bacteria, the so-called facultative anaerobes, for which oxygen is toxic. It has been proposed that these were among the very first types of life forms that arose on planet Earth. One can carry out interesting observations on samples which one allows to gradually foul. It is quite remarkable that a number of macro- and micro-invertebrates, protozoa, and bacteria will survive until conditions become so extreme as to be lethal. I have found cladocerans, ostracods, and bdelloid rotifers surviving in surprising conditions, sometimes swimming and feeding rapidly in spite of the fact that they were furry with mold.
Here is a typical cladoceran that shows such survival skills.
And a typical ostracod:
As I mentioned earlier, the water in the lakes and ponds here is highly alkaline, but that is no ultimate deterrent to life since there is a bacterium, Bacillus alcalophilus, which has been found in environments in which the pH exceeds 10!!!
Bacteria, algae, and cyanobacteria have been found in contexts that are not only highly alkaline but extremely hot as well. The hot springs, mud pots, and geysers in places such as Yellowstone provide a wide variety of examples.
An amazing phenomenon is that we can usually find organisms which exist at the opposite extreme. There are algae and bacteria which thrive in acidic waters which is a considerable concern to environmentalists. Cold is also dealt with by a variety of organisms using ingenious techniques. Some creatures have developed a kind of antifreeze which prevents ice from forming in cells and tissue and puncturing the membranes. Lichens may be the champions when it comes to adapting to temperature extremes. These are very bizarre life forms; actually they are a peculiar conjoining of two life forms: 1) a photosynthetic micro-organism (either an alga or a cyanobacterium) and 2) a fungus. Lichens are very encouraging to exobiologists because they have able to survive in environments with temperatures ranging from -200 C. to +80 C. !!!
Pressure is another challenge which certain life forms have taken on and dealt with successfully. It used to be thought that the abyssal plains of the oceans were barren deserts, but recent investigations have shown both an abundance and a wide variety of life forms living at pressures that are staggering to the human mind.
As researchers investigate, they find more and more examples of mind-boggling extremes. Bacteria which metabolize hydrocarbons and thus may be of value in dealing with oil spills; bacteria which metabolize one form of uranium reducing it to a more stable, and thus less dangerous, form; and salt-loving bacteria that have been dated to 250 million years in age.
See this 'Letter to Nature'.
Much of this seems like the stuff of science fiction, but perhaps that is because life itself is so utterly bizarre and we still have so much to learn. In 2011, National Geographic published an article in which is reported that thus far we have only identified about 15 percent of the life forms on our planet.
Clearly, few of us are equipped to investigate the most extreme of the extremophiles, but the more moderate forms are abundant and many are quite accessible and understanding their adaptive strategies may be of considerable importance in the future.
All comments to the author Richard Howey are welcomed.
Editor's note: Visit Richard Howey's new website at http://rhowey.googlepages.com/home where he plans to share aspects of his wide interests.
Microscopy UK Front
Published in the May 2014 edition of Micscape Magazine.
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