Alkaliphiles: Ecology, diversity and applications

Abstract

Organisms with pH optima for growth in excess of pH8, usually between 9 and 10, are properly defined as alkaliphiles (or sometimes alkalophiles). Most of the organisms described to date as growing under very alkaline conditions are prokaryotes, comprising a heterogeneous collection of eubacteria (including cyanobacteria) with a few examples of archaebacteria. With the exception of the alkaliphilic archaebacteria (which are also halophilic), few of the isolates have been comprehensively classified. However, it is clearly that may different taxa are represented amongst the alkaliphiles, and that some of these at least are likely to be new taxa. Alkaliphiles can be isolated from ‘normal’ environments such as garde soil, presumably because there are transient alkaline conditions generated in such environments by biological activity, but a relatively restricted range of types results from the exploration of such environments (often Bacillus spp.). Naturally-occurring stable alkaline environments such as eutrophic soda (Na2CO3) lakes harbour a much wider range of types. A similarity wide range of types may exist in oligotrophic Ca(OH)2-dominated ground water in certain parts of the world. Alkaliphilic microorganisms have already made a large impact in the application of biotechnology for the manufacture of mass market consumer products. “Biological detergents” contain enzymes that have usually been obtained from alkaliphilic or alkalitolerant bacteria. The current proportion of total world enzyme production destined for the laundry detergents market comfortably exceeds 25%, and there are other possible applications in food and waste treatment industies. To date, most commercially available enzymes are derived from a few bacterial taxa (notably Bacillus spp.) and we have been very conservative in our choice of environments in which to look for new products. It is reasonable to suppose that soda lakes (and other alkaline environments) will yield a wealth of new organisms with useful commercial properties.