Nitrite reduction in Rhizobium "hedysari" strain HCNT1.

Rhizobium \u201chedysari\u201d strain HCNT 1 rapidly reduced nitrite to N2O, only slowly reduced nitrate to nitrite and did not exhibit nitrous oxide reductase activity. Nitrite reduction in this rhizobium strain may be a detoxification mechanism for conversion of nitrite, which inhibits O2 uptake, to non-toxic N2O. Concentrations of nitrite as small as 3 \ub5M diminished O2 uptake in whole cells. The bacterium did not couple energy conservation with nitrate or nitrite reduction. Cells neither grew anaerobically at the expense of these nitrogen oxides nor translocated protons during reduction of nitrite. Induction of nitrite reductase activity was not a response to the presence of nitrate or nitrite, but occurred instead when the O2 concentration in culture atmospheres fell to o, which is synthesized only in cells grown under O2-limited conditions, may account for the toxicity of nitrite in strain HCNT 1