Open AccessThe metabolism of hydrogen by extremely thermophilic, sulfur‐dependent bacteria
Author(s) -
Adams Michael W.W.
Publication year - 1990
Publication title -
fems microbiology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.899
H-Index - 151
eISSN - 1574-6968
pISSN - 0378-1097
DOI - 10.1111/j.1574-6968.1990.tb04096.x
Subject(s) - thermophile , hydrogenase , mesophile , pyrococcus furiosus , bacteria , sulfur , extremophile , archaea , psychrophile , biology , biochemistry , enzyme , energy source , chemistry , ecology , organic chemistry , genetics , renewable energy
In just the last few years, a group of bacteria have been discovered that have the remarkable property of growing near and above 100°C. These extremely thermophilic organisms, defined here as having the ability to grow at 90°C with optimum growth at 80°C and above, have been isolated mainly from sulfur‐rich, marine geothermal environments, both shallow and deep sea. They comprise over a dozen different genera, and except for one novel eubacterium, all may be classified as archaebacteria. The majority of the extremely thermophilic genera metabolize elemental sulfur (S°) and a survey of the various organisms reveals that most of them also depend upon the oxidation of hydrogen gas (H 2 ) as an energy source. In addition, two extremely thermophilic genera are known that actively produce H 2 as end‐products of novel fermentative metabolisms. The enzyme hydrogenase, which is responsible for catalysing H 2 activation and H 2 production, appears to play several roles in electron and energy transfer during the growth of these organisms. Hydrogenase has so far been purified from only one extremely thermophilic species, from Pyrococcus furiosus ( T opt = 100°C), and hydrogenase activity has been exmained in cell‐free extracts of only a few others. However, a comparison of their properties with those of hydrogenases from mesophilic bacteria suggests that (a) the hydrogenase responsible for catalysing H 2 oxidation in extremely thermophilic organisms may be an extremely thermostable version of the mesophilic enzyme, and (b) a new type of ‘evolution’ hydrogenase, lacking the Ni‐S or Fe‐S catalytic sites of the mesophilic enzymes, is required for catalysing H 2 evolution at temperatures near and above 100°C.