Microbe Monday #1: Life in a Freezing Desert

Each week, new bacteria and other microbes are described in the International Journal of Systematic and Evolutionary Microbiology. Most days, papers are published online closed to midnight my time (EST). So, if I write about them the next day, they are technically betraying the rules of this blog: I write about new species, the same day their descriptions are published.

The result of this is that, with much regret, I have been neglecting bacteria on this blog. No longer! From now on, each Monday I will write about my favorite new species of bacteria (or other microbe) that was published the week prior. Last week’s new species, Saccharibacillus deserti, was the one that convinced me. This amazing bacterium is most unusual for the place it lives: the frigid deserts of northern China (Sun et al. 2015).

The Taklamakan Desert in Xinjiang Province. Photo by Colegota, licensed under CC BY-SA 2.5 ES.

The Taklamakan Desert in Xinjiang Province. Photo by Colegota, licensed under CC BY-SA 2.5 ES.

Deserti was discovered in the upper layers of soil in the Ordos Desert, in Inner Mongolia (a province in China, not Mongolia). On a yearly basis, there is less than 9 inches of rain, and almost all of this falls during a series of storms in the summer months. The Ordos is not only dry, but also cold, with winter temperatures consistently below 10º F.

The new species’s close relative, S. kuerlensis, has it even worse (Yang et al. 2009). The deserts near Kuerle (Xinjiang province, China) are similarly cold in winter, but even drier, with and average annual rainfall of less than 3 inches.

Bactrian camels in Mongolia. Photo by Yaan, licensed under CC BY-SA 3.0.

Bactrian camels in Mongolia. Photo by Yaan, licensed under CC BY-SA 3.0.

Because they are so inhospitable, the cold deserts of central Asia are home to very few large animals. The best-known is the Bactrian camel, whose thick insulating fur and fat-storing humps allow it to survive long periods without eating or drinking. Still, camels have to migrate long distances to find enough food and water to last the winter.

Bacteria are, of course, not migratory. So how does a desert-dwelling bacteria survive between rains? They form endospores, protective structures that allow them to go dormant, “hibernating” until warmth and moisture wake them back up again.

The protective endospore does not form on the outside of the bacterium, as you might expect, but on the inside of the cell — hence the prefix “endo,” meaning inside. The spore exists only to protect the most important parts of the cell, such as the DNA, ribosomes (molecules used to translate genetic information into proteins), and a few choice chemicals that help prevent everything from degrading when subject to heat, cold, or drought. One of these chemicals is calcium dipicolinate, which helps to prevent DNA from degrading when subject to harsh conditions.

Because the endospore only forms around the nucleoid of the cell, only the most vital parts of the bacterium are protected. Everything outside the endospore withers away, but when conditions are right again (e.g., summer rains come to northern China) the endospore breaks down and the DNA, RNA, and ribosomes get to work rebuilding what is lost. Because all the DNA is saved, the bacterium still has all the information it needs to re-create itself.

Cited:

Sun J.Q., X.Y. Wang, L.J. Wang, L. Xu, M. Liu, and X.L. Wu. 2015. Saccharibacillus deserti sp. nov., isolated from desert soil. International Journal of Systematic and Evolutionary Microbiology doi: 10.1099/ijsem.0.000766.

Yang S.Y., H. Liu, R. Liu, K.Y. Zhang, and R. Lai. 2009. Saccharibacillus kuerlensis sp. nov., isolated from a desert soil. International Journal of Systematic and Evolutionary Microbiology 59: 953-957.

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