Diversity and Mechanisms of Adaptation of Predominant Bacterial Chemolithotrophs in Extreme Habitats

 Bacterial chemolithotrophy is one of the most ancient metabolisms and is generally defined as the ability of some microorganisms to utilize a wide range of inorganic substrates as an energy or electron source. While lithotrophy can itself be considered as extremophily, as only some microorganisms (the rock-eaters) have the ability to utilize diverse inorganic chemicals as the sole source of energy, the phylogenetically diverse groups of lithotrophs can thrive in a wide range of extreme habitats. Apart from their excellent eco-physiological adaptability, they also possess versatile enzymatic machinery for maintaining their lithotrophic attributes under such extreme environments. In this chapter, we have highlighted the diversity of iron, hydrogen and sulfur lithotrophic extremophilic bacteria in various extreme habitats, and their role in maintaining the primary productivity, ecosystem stability and mineral cycling / mineralogical transformations. Moreover, genetic determinants and different enzymatic systems which are reported to be involved in such lithotrophic metabolism also have been discussed. We hope this article will shed some new light on the field of extremophile lithotrophy, which will eventually improve our understanding of the extended new boundaries of life.