Extreme Ecosystems - A Tough Bunch of Microbes!

Hoover and microbiologist Elena Pikuta of the University of Alabama in Huntsville are working to answer some of these questions by studying lifeforms in California's Mono Lake. They recently announced the discovery of a third new species of bacteria, Desulfonatronum thiodismutans, living in the lake in the International Journal of Systematic and Evolutionary Microbiology. All three of Pikuta and Hoover's new species are extremophiles. The bacteria thrive in the dark mud of Mono Lake, devoid of oxygen with 3 times higher salinity than sea water and alkalinity that approaches lye.

This third new species is particularly interesting because of its niche in the extreme ecology of the lake. This bacterium obtains its energy from sulfur and other inorganic compounds. It does not require sunlight or other organic materials to thrive and is a type of organism known as a chemolithotroph. Hoover and Pikuta's two previous new species, Tindallia californiensis and Spirochaeta americana are also extremophiles from Mono Lake, but ingest organic materials. These organisms are known as organotrophs. Together they paint a picture of interlinked and interdependent life, even under extreme conditions.

Richard Hoover collects samples from the mud of Mono Lake.

For example, D. thiodismutans gets its energy from hydrogen and sulfur compounds in the minerals of the lake mud. From these it creates sugars and other organic materials. T. californiensis can consume simple amino acids and other chemicals and also produces complex organic compounds such as sugars, fats, proteins, etc. S. americana ingests the complex organic compounds and excretes hydrogen and other gases. When it dies, it returns to minerals and the cycle is complete.

Unlike the plant/animal cycle in our "normal" environment, this bacterial cycle does not necessarily need visible energy from sunlight to drive photosynthesis. It can be driven completely by the chemical energy of the reactions. So in a dark, extreme environment, life appears to develop the same interdependent strands, with different species finding the niche that allows each to thrive.

One day, perhaps, lifeforms like these will be found on other worlds. The work of Hoover and Pikuta is telling us that if we find one species, we should look for more. Extremophiles, like "ordinary" lifeforms, don't like being alone.