Alkaliphilic prokaryotes

Abstract

Alkaliphilic bacteria are widely distributed extremophiles, some of which grow in alkaline niches in which the pH is above 12. These niches include alkaline soda lakes, which are found throughout the world, providing natural enrichments for an impressively diverse array of alkaliphiles. They are also found in more specialized alkaline niches such as the hindguts of certain insects, as well as in soil, marine, and man-made niches. Alkaliphiles are represented in a large number of bacterial genera and physiological types, but share common challenges that include cytoplasmic pH homeostasis and associated problems of bioenergetic work, function of surface-associated and secreted proteins that must function at very high pH, and acquisition of iron and other ions that are at low bioavailability. Studies of the solutions used by alkaliphiles to solve these problems have provided fundamental biological insights and identified transporters and channels that have impact beyond alkaliphiles, including the Mrp family of antiporters, the NaChBac family of channels, and two new types of flagellar stator channels. Alkaliphile enzymes have long been applied to diverse biotechnological uses. There is great potential for expanded use of both alkaliphile enzymes and other products because of the rapid pace of identification of new alkaliphiles, the availability of genomic and metagenomic data, and increasing insights into adaptations involved in alkaliphily obtained from combined structural and phylogenetic data. Through molecular bioengineering, these insights can be tested and applied. Similarly, the expansion of information about the capabilities of alkaliphiles promises increasing use of the organisms themselves in bioprocessing and bioremediation settings.