Denitrification by a diazotrophic Pseudomonas species

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 [Formula: see text] was reduced to [Formula: see text]. In the present study it grew anaerobically with [Formula: see text], [Formula: see text], or N2O as electron acceptor. Its capability to denitrify was confirmed by using the C2H2-inhibition technique in both undefined and defined media with glucose as carbon source. Chemolithotrophic denitrification of [Formula: see text] 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[Formula: see text] Compared with Azospirillum brasilense, a N2-fixing bacterium capable of denitrification, H8 was not sensitive to [Formula: see text] toxicity under similar experimental conditions. Preliminary evidence suggested that N2O reduction by H8, but not by A. brasilense, was inhibited by yeast extract. The denitrification capability of H8 may prove to be an undesirable characteristic that leads to the removal of [Formula: see text] N from soils.