EFFECT OF NITRATE ON REDUCTION OF FERRIC IRON BY A BACTERIUM ISOLATED FROM CRUDE-OIL

A Pseudomonas sp. isolated from crude oil reduced Fe(III) to Fe(II). In the presence of NO3- after prolonged incubation, the amount of Fe(II) was lower than in its absence. During short incubation periods, the presence of NO3- significantly increased (99.5% confidence limit) the amount of Fe(II) produced. The decrease in Fe(II) on prolonged incubation was associated with increased production and accumulation of nitrite (NO2-). Under low NO3- levels, where the production of NO2- was limited, a decrease in NO2- concentration was accompanied by an increase in Fe(II) production to levels comparable with those obtained in the absence of NO3-. Preinduction of cells for nitrate reductase, which favored rapid NO2- production, resulted in a more rapid decrease in Fe(II) production than in cells that were not preinduced. The inhibitory effect of NO3- on microbial reduction of Fe(III) is probably due to a secondary reaction, which involves the chemical oxidation of Fe(II) by NO2-.