Microorganisms have optimal environmental conditions under which they grow best. Classification of microorganisms in terms of growth rate dependence on temperature includes the thermopiles, the mesophiles and psychrophiles. Similarly, while most organisms grow well in neutral pH conditions, some organisms grow well under acidic conditions, while others can grow under alkaline conditions. The mechanism by which such control exists is being studied in detail. This will overcome the need to obtain mutants by a slow and unsure process of acclimatization.

When some organisms are subjected to high temperatures, they respond by synthesizing a group of proteins that help to stabilize the internal cellular environment. These, called heat shock proteins, are present in both prokaryotes and eukaryotes. Heat stress specifically induces the transcription of genes encoding these proteins. Comparisons of amino...