Living on Air


Breaking down the microbiology world one bite at a time

Living on Air

One of my not-so-favorite parts of having ice cream is the brain freeze. Just imagine if I ask you to live with that feeling for not a few moments but for as long as you could think of. I am sure that you won’t be happy about it. Just like you, organisms would neither like that feeling nor like to live on the coldest continent of the planet, Antarctica.

Almost all living organisms would appreciate living conditions where everything is just right – the right temperature, salt concentration, light, and availability of food resources. However, the frigid land of Antarctica challenges life by presenting unfavorable conditions such as extremely low temperature, unavailability of food and water, and light-dark seasonality.

Under an amicable environment, the producers of the ecosystem, generally green plants, use sunlight to fix the carbon dioxide from the surroundings into a simple molecule: glucose (organic carbon). Glucose is then used as the primary energy source by the producers themselves, which are photoautotrophs (photoautotrophs = photo →light + auto →self + troph →nourishment), followed by successive levels in the food web. Those who cannot make their own food rely on others and are called heterotrophs (heterotrophs = hetero →other + troph →nourishment). Some organisms would directly eat producers, whereas others prey on these producer-eating organisms. However, Antarctica’s climate doesn’t facilitate such dynamics.

These stressful living conditions drive away most of the larger creatures. Nevertheless, it turns out that microscopic beings are pretty adjustable and can survive in the harsh climate of Antarctica.

Ortiz and Leung’s team studied soil from 16 sites in Antarctica. Despite astonishingly low organic carbon content, the soil was home to a remarkable number of bacteria and similar organisms. The composition of the community in the samples varied. Moreover, the sampled bacteria are indigenous to Antarctic soil and could have evolved from 700-880 million-year-old organisms native to the soil. Given the poor living conditions, how do these bacteria get food and water – how do they survive?

The researchers’ genetic and biogeochemical analyses reveal diverse strategies adopted by the bacteria to gain access to nutrition. First, almost all members of the community perform respiration in the presence of oxygen rather than in its absence. Next, many members resort to a mix of autotrophy and heterotrophy (mixotrophs). Interestingly, the abundant organisms derive energy from certain gases in the atmosphere, an unlimited source of gases, to obtain energy-rich molecules mainly by oxidizing hydrogen and/or carbon monoxide. Some bacteria can also oxidize methane. What’s more, oxidation of atmospheric hydrogen helps these bacteria produce water! This mechanism of water production can help these bacteria in staying hydrated.

The figure is a schematic representation of the experimental design used by the researchers.

Therefore, even in the shortage of organic carbon or water that allows transport of non-gaseous molecules, these bacteria can persist.

Apart from these strategies, bacteria have other ways to find nutrients. More than 25% of the community members can fix atmospheric carbon through the Calvin cycle, a method of carbon fixation in the absence of light. This process would help these bacteria to survive even in low levels of sunlight. And actually, only very few organisms had the machinery to use sunlight to gain nourishment. Furthermore, some bacteria from the Antarctic soil can also oxidize trace amounts of ammonium, sulfur, and iron in the soil. Surprisingly, the soil also harbored diverse bacteria that were either predators, parasites, or obligate symbionts.

The diverse ways adopted by the bacteria to survive in the unfriendly environment of Antarctica are fascinating. Such studies are not only awe-inspiring but they also help humanity to progress. First, considering the effects of climate change on the Antarctic landscape, such studies help us in making decisions that would save the continent’s environmental future. Second, scientists are able to know more about how life evolved in Antarctica. This knowledge is crucial because it helps us understand how life could develop and sustain on other cold, dry planets such as Mars!

Brain freeze isn’t that bad after all!

Link to the original post: Maximiliano Ortiz, Pok Man Leung, Guy Shelley, Thanavit Jirapanjawat, Philipp A. Nauer, Marc W. Van Goethem, Sean K. Bay, Zahra F. Islam, Karen Jordaan, Surendra Vikram, Steven L. Chown, Ian D. Hogg, Thulani P. Makhalanyane, Rhys Grinter, Don A. Cowan, Chris Greening, Multiple energy sources and metabolic strategies sustain microbial diversity in Antarctic desert soils, Proceedings of the National Academy of Sciences Nov 2021

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