Oxidative consumption of nitric oxide by heterotrophic bacteria in soil

Abstract

Uptake rate constants for nitric oxide were measured in a neutral calcic cambisol (KBE) and an acidic luvisol (PBE). The NO uptake was higher under oxic than under anoxic incubation conditions by a factor of about three. Gassing the soils with air containing 10 ppmv NO resulted in the accumulation of nitrate which accounted for 57–94% of the NO consumed. Aerobic heterotrophic bacteria were isolated on glucose-yeast extract medium from soil dilutions corresponding to a most probable number of 108–109 bacteria per gram dry weight soil. One of the isolates (strain PS88, a Pseudomonas sp.) exhibited NO consumption activity that was much higher under oxic than anoxic incubation conditions. When sterile KBE amended with strain PS88 was gassed with air containing 10 ppmv NO, 88% of the consumed NO was recovered as nitrate and nitrite. A screening of various bacteria obtained from culture collections showed a widespread ability for consumption of low NO concentrations. Our results indicate that NO consumption in soil is not only possible by reductive denitrification, but also by oxidation due to aerobic heterotrophic bacteria such as strain PS88.