Denitrification by a diazotrophic Pseudomonas species

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Abstract
Pseudomonas sp. type strain H8 is a N2-fixing H2-utilizing bacterium frequently isolated from the root of wetland rice. It was previously reported not to denitrify although NO3- was reduced to NO2-. In the present study it grew anaerobically with NO3-, NO2-, or N2O as electron acceptor. Its capability to denitrify wsa confirmed by sing the C2H2-inhibition technique in both undefined and defined media with glucose as carbon source. Chemolithotrophic dentrificaiton of NO3- with H2 and CO2 was also demonstrated.Its H2-uptake activity was found to be higher when grown initially in the presence of 10% O2 than 21% O2 or 5 mM NO3-. Compared with Azospirillum brasilense, a N2-fixing bacterium capable capable of dentrification, H8 was not sensitive to NO3- toxicity under similar experimental conditions. Preliminary evidence suggested that N2O reduction by H8, but not by A. brasilense, was inhibited by yeast extract. The dentrification capability of H8 may prove to be an undesirable characteristic that leads to the removal of NO3- N from soils.