Biodegradation of monohalogenated alkanes by soil NH3-oxidizing bacteria

摘要

Although cooxidative biodegradation of monohalogenated hydrocarbons has been well studied in the model NH3-oxidizing bacterium, Nitrosomonas europaea, virtually no information exists about cooxidation of these compounds by native populations of NH3-oxidizing bacteria. To address this subject, nitrifying activity was stimulated to 125–400 nmol NO3 – produced g–1 soil h–1 by first incubating a Ca(OH)2-amended, silt loam soil (pH 7.0±0.2) at field capacity (270 g H2O kg–1 soil) with 10 µmol NH4 + g–1 soil for 14 days, followed by another 10 days of incubation in a shaken slurry (2:1 water:soil, v/w) with periodic pH adjustment and maintenance of 10 mM NH4 +. These slurries actively degraded both methyl bromide (MeBr) and ethyl chloride (EtCl) at maximum rates of 20–30 nmol ml–1 h–1 that could be sustained for approximately 12 h. Although the MeBr degradation rates were linear for the first 10–12 h of incubation, they could not be sustained regardless of NH4 + level and declined to zero over 20 h of incubation. The transformation capacity of the slurry enrichments (~1 µmol MeBr ml–1 soil slurry) was similar to the value measured previously in cell suspensions of N. europaea with similar NH3-oxidizing activity. Several MeBr-degrading characteristics of the nitrifying enrichments were found to be similar to those documented in the literature for MeBr-degrading methanotrophs and facultatively methylotrophic bacteria.