Extremophiles: Hot Environments

Relationship between Organisms and their Environment

The high temperatures and geochemistry found in terrestrial and marine geothermal sites are unique. Volcanically derived gases and products from water–rock reactions support chemolithoautotrophic-based microbial communities in what has been termed the deep, hot biosphere. Endolithic microbial communities are pervasive in these environments and likely contribute significantly to subsurface biomass production, which may constitute a significant portion of the total biomass on the planet. The subsurface biosphere is a largely unknown and untapped natural resource. Thermophiles and hyperthermophiles inhabit these environments and serve as model organisms for microbial processes that occur at high in situ temperatures. Although known hyperthermophiles may comprise only a small minority of the total microbial population in a geothermal environment, their metabolisms are likely reflections of the kinds of processes occurring within them. Because they are typically not found in nongeothermal background fluids, they can serve as tracers of in situ chemical and physical conditions within geothermal environments.

Before one can use these organisms as models of biogeochemical processes in geothermal environments, there are a number of fundamental questions that must be addressed related to the relationship between high-temperature organisms and their environment. For example, what are the physical and chemical constraints on metabolic processes? Are different forms of thermophile and hyperthermophile metabolism spatially and temporally segregated on the basis of fluid chemistry? Clearly, the presence of thermoacidophiles, thermoneutrophiles, and thermoalkaliphiles shows how pH can influence microbial distributions and metabolisms, but can these types of changes be observed on a finer scale even within the same organism? What are the different ways in which organisms assimilate CO2or respire a given compound? Are these differences rooted in environmental factors that favor one metabolism over another? Many hyperthermophiles have a requirement for tungsten to meet the needs of certain enzymes found in central metabolic pathways. Are there other unique cofactors used by these organisms? What do these mean with respect to the natural history of these organisms?

In conclusion, extremophiles from hot environments have moved from mere curiosity to a group of organisms that have significant medical and biotechnological applications and are useful for the study of the evolution and biochemistry of metabolic pathways and the biogeochemistry of geothermal environments. Many thermophiles and most hyperthermophiles belong to the Archaea, which is the third superkingdom of life for which there is still much to be learned. Because physiology and ecology go hand in hand, the continued study of high-temperature organisms from these two perspectives should expand our appreciation for these organisms and the function they have in nature.

Reproduced from. 

J.F. Holden in Encyclopedia of Microbiology, 2009