ABSTRACT
The study of biodiversity is a relatively recent subject concerned not only with recording and monitoring changes in the diversity of life but also with the levels on which biology is organised and the interrelationships between them. Biodiversity is measured on three fundamental levels: ecosystems, species and genes. Questions concerning evolutionary relationships underlie all of biodiversity. This chapter considers the biodiversity of H2 metabolism by reviewing the species in which H2 metabolism has been studied, the importance of H2 metabolism to those organisms and to different ecosystems, and the occurrence, function and evolution of different hydrogenases and the genes which encode them. Questions concerning the analysis of the diversity of H2 metabolising bacteria in different environments and the potential existence of novel systems are also considered.
