ABSTRACT
A fundamental question is whether microorganisms that thrive near the upper temperature limit for life (currently 113 "C; Blochl et al., 1997) require unusual growth substrates, substances not typically needed by more conventional life forms. If so, what are such substances used for, and do they have any evolutionary significance? In this chapter we focus on the utilisation of the metals tungsten (W, atomic number 74) and molybdenum (Mo, 42) by microorganisms that grow at 100 ·c. These two elements are chemically analogous but they have very different biological functions, and microorganisms growing at extreme temperatures have been central in our understanding of why biological systems differentiate between tungsten and molybdenum. The reader is referred to the recent reviews on the role of tungsten (Kletzin and Adams, 1996; Johnson et al., 1996) and molybdenum (Hille, 1996; Howard and Rees, 1996) in biological systems and the properties of enzymes that contain these elements.
