OXIDATIVE CONSUMPTION OF NITRIC-OXIDE BY HETEROTROPHIC BACTERIA IN SOIL

Uptake rate constants for nitric oxide were measured in a neutral calc ic cambisol(KBE) and an acidic luvisol (PBE). The NO uptake was higher under oxic than under anoxic incubation conditions by a factor of abo ut three. Gassing the soils with air containing 10 ppmv NO resulted in the accumulation of nitrate which accounted for 57-94% of the NO cons umed. Aerobic heterotrophic bacteria were isolated on glucose-yeast ex tract medium from soil dilutions corresponding to a most probable numb er of 10(8)-10(9) bacteria per gram dry weight soil. One of the isolat es (Strain PS88, a Pseudomonas sp.) exhibited NO consumption activity that was much higher under oxic than anoxic incubation conditions, Whe n sterile KBE amended with strain PS88 was gassed with air containing 10 ppmv NO, 88% of the consumed NO was recovered as nitrate and nitrit e. A screening of various bacteria obtained from culture collections s howed a widespread ability for consumption of low NO concentrations. O ur results indicate that NO consumption in soil is not only possible b y reductive denitrification, but also by oxidation due to aerobic hete rotrophic bacteria such as strain PS88.