EFFECT OF NITROGEN-SOURCE ON GROWTH AND TRICHLOROETHYLENE DEGRADATIONBY METHANE-OXIDIZING BACTERIA

The effect of nitrogen source on methane-oxidizing bacteria with respe ct to cellular growth and trichloroethylene (TCE) degradation ability were examined, One mixed chemostat culture and two pure type II methan e-oxidizing strains, Methylosinus trichosporium OB3b and strain CAC-2, which was isolated from the chemostat culture, were used in this stud y. All cultures were able to grow with each of three different nitroge n sources: ammonia, nitrate, and molecular nitrogen. Both M. trichospo rium OB3b and strain CAC-2 showed slightly lower net cellular growth r ates and cell yields but exhibited higher methane uptake rates, levels of poly-beta-hydroxy-butyrate (PHB) production, and naphthalene oxida tion rates when grown under nitrogen-fixing conditions. The TCE-degrad ing ability of each culture was measured in terms of initial TCE oxida tion rates and TCE transformation capacities (mass of TCE degraded/bio mass inactivated), measured both with and without external energy sour ces. Higher initial TCE oxidation rates and TCE transformation capacit ies were observed in nitrogen-fixing mixed, M. trichosporium OB3b, and CAC-2 cultures than in nitrate- or ammonia-supplied cells. TCE transf ormation capacities were found to correlate with cellular PHB content in all three cultures. The results of this study suggest that the nitr ogen fixing capabilities of methane-oxidizing bacteria can be used to select for high-activity TCE degraders for the enhancement of bioremed iation in fixed-nitrogen-limited environments.