[Denitrification in a sporulating thermophilic bacterium].

Denitrification in a thermophile isolated on nitrite containing-medium (5 g/l) was studied by means of Warburg respirometry and gas chromatography. This strain seems to denitrify nitrite more rapidly than nitrate. Extracts of cells grown anaerobically on nitrate have dissimilatory nitrate reductase (type A); extracts of cells grown aerobically without nitrate have raised levels of the two types of nitrate reductase A and B. The optimal temperature for enzyme A activity is 60 degrees C. Nitrite reductase activity was measured using yeast extract as electron donor. For nitric oxide reductase activity, yeast extract is as efficient an electron donor as sodium lactate. Nitrous oxide reductase activity was found only in the 4 000 g supernatant showing the particulate nature of the enzyme. A mixture of FAD, FMN and NADH served as electron donor. Using acetylene as an inhibitor of nitrous oxide reduction in both whole cells and extracts, we showed that this gas is an intermediate compound in the reduction of NO to N2.