Abstract

Extremophilicity, or the capability to thrive in environmental conditions considered extreme is generally determined from the human perspective. From that point of view, organisms adapted to scarce, or even the absence of molecular oxygen, can be considered as one of the extremophiles, i.e., anaerobes. In this chapter, various aspects of anaerobic microorganisms are addressed, including their different taxa, their phylogenetic distribution, and the environments from where they have been isolated. Since prokaryotic taxonomy is a dynamic process, here we have emphasized the organisms that are validly placed in taxa and have cultured representatives. In this section, Archaea and Bacteria - the two domains are separately discussed. Similar separation is also maintained while discussing mechanisms of adaptation, as far as possible. Since these two domains share certain properties, the subsequent sections are not separated between these two domains.