Microbial Adaptation to Extremes of Temperature and pH
The question I would like to raise in this brief article is whether there are fundamental physical and chemical limitations on the evolution of organisms able to grow under extreme environmental conditions such as we find in polluted situations. The specific environmental factors I would like to consider are high temperature and low pH, and high temperature and low pH taken together. Temperature and hydrogen ion concentration are probably the most basic environmental factors which organisms must cope with, and both natural and polluted environments exist in which these factors exist in the extreme. The attitude and approach here is quite different than that of the physiologist or biochemist, who looks at how a given organism responds to environmental change. We are interested in how living organisms, taken as totality, respond. This means we must look at stable natural environments which have been available for colonization for millions of years, so that we know there has been time for evolution to reach an equilibrium. We thus study natural thermal and acidic springs, since these provide relatively constant environments of types which have probably been available for colonization as long as life has been present on earth. Much of our own work has been reviewed recently (Brock, 1967, 1969, 1970) so that in the present paper I will give only an outline of past studies and concentrate on recent studies which have not yet been published. To simplify the discussion, I will consider high temperature and low pH separately, and then consider the two factors together.
KeywordsPhotosynthetic Membrane Environmental Condi Tions Lower Temperature Form Specific Environmental Factor Microbial Adaptation
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