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Chapter 2 : Thermal Environments and Biodiversity
Category: Applied and Industrial Microbiology; Environmental Microbiology
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This chapter summarizes some of the thermal environments on Earth and describes the taxonomic, genetic, metabolic, and ecological diversity of these environments. Biogeology/biogeochemistry is especially of interest in thermal environments, where mineralization is active and the role of prokaryotes in mineralization is being examined. Water is readily available in circumneutral, freshwater hot springs, but there are thermal environments having low water potentials; e.g., in intraterrestrial environments because of high surface area-to-water ratios or in solar heated soils and sediments because of evaporation and high salinity. The authors believe that many environments that are classified as mesobiotic from their bulk temperature measurements contain temporary thermal microniches, created by localized biodegradation of organic material. Measuring the genetic diversity of 16S rRNA and functional genes, which has been an avenue for discovery of many enzymes for biotechnological applications and the isolation of novel microorganisms, provides only limited information about their in situ abundance and activity. In general, analysis of multiple approaches applied in single environments combined with that of similar approaches in different environments has enhanced the robustness of our understanding of the various high-temperature environments and the biodiversity they harbor. Considering how the initial discovery of life in shallow and deep-sea vents expanded our notion of global biodiversity, future approaches and discoveries, perhaps also in extraterrestrial thermal environments, will likely reveal additional information relevant to many fields of basic and applied science.
Thermophilic archaea: aerobic/microaerophilic/facultative aerobic archaea (◯) and anaerobic/facultative aerobic archaea (∎). A, P. oshimae and P. torridus: optimal growth at pH 0.7, 60°C ( Schleper et al., 1995 ). B, P. fumarii: optimal growth at 106°C, pH 5.5 ( Blochl et al., 1997 ). C, Thermococcus acidaminovorans: optimal growth at pH 9, 85°C ( Dirmeier et al., 1998 ).
Thermophilic bacteria: aerobic/microaerophilic/facultative aerobic bacteria (◯) and anaerobic/facultative aerobic bacteria (∎). D, Alicyclobacillus hesperidum: optimal growth at pH 3.5–4.0, 50–53°C ( Albuquerque et al., 2000 ). E, Aquifex pyrophilus: optimal growth at 85°C, pH 6.8 ( Huber et al., 1992 ). F, C. paradoxum: optimal growth at pH25°C 10.1, 55–56°C ( Li et al., 1993 ).
Comparison of richness of restriction enzyme phylotypes (types) from clone libraries of environmental 16S rRNA genes from a small selection of thermal environments