Novel approaches to exploit microbial hydrogen metabolism

Publisher Summary The key enzyme in biological hydrogen (H 2 ) metabolism is hydrogenase, which catalyzes the formation and decomposition of H 2 . Hydrogenases are metalloenzymes harboring Ni and Fe, or only Fe atoms, arranged in an exceptional structure. This chapter focuses on the hydrogenases with NiFe active centers. The best sources of hydrogenases, both for basic research and for forthcoming large-scale utilization, are micro-organisms that are cheap to cultivate and use sunlight to get energy for their growth. Thiocapsa roseopersicina ( T. roseopersicin ), which is a phototrophic bacterium, is one of the best candidates for studies of NiFe hydrogenase structure-function relationships and assembly because it contains four distinct NiFe hydrogenase molecular species. Methane-oxidizing bacteria (methanotrophs) have attracted considerable interest over the past twenty years because of their potential in producing bulk chemicals (e.g., propylene oxide) and single-cell protein and for use in biotransformation. Methanotrophs oxidize methane using the enzyme methane monooxygenase (MMO). Methanotrophic bacteria utilize H 2 to supply reductant for their MMO enzyme systems. H 2 driven enzyme activity plays a determining role in methane oxidation. Decomposition of wastes anaerobically to form biogas is one of the earliest applications of biotechnology, and H 2 has an important role in anaerobic fermentation. This chapter discusses the results of a few experiments that were conducted to test whether H 2 is a rate limiting substrate for methanogens.