Isolation, Identification And Characteristics Of A Nitrobenzene-Degrading Bacterium XY-1

A bacterial strain capable of degrading nitrobenzene efficiently was isolated from nitrobenzene-contaminated soil. This bacterium was identified preliminarily as Pseudomonas sp. based on its morphous, physiological & biochemical characters and 16S rRNA sequence analysis, it was designated as XY-1.The optimal temperature for the growth of strain XY-1 was 30℃, the optimal pH value was 6.0～10.0. The optimal concentration of NaCl for the strain XY-1 was 0.5-15 g/L. The optimal medium for the growth of strain XY-1 was glucose, maltose and sucrose as carbon source and organic nitrogen as nitrogen source. XY-1 had resistance to 100 mg/L of ampicillin, actinospectacin, streptomycin, chloromycetin and erythromycin.Strain XY-1 could grow with nitrobenzene as its sole carbon source, the rate of degrading nitrobenzene with its preliminary concentration of 200 mg/L arrived at 97% within 24 h. The optimal pH value for nitrbenzene degradation by XY-1 was 7.0～9.0, the optimal temperature was 30℃. The rate of degrading nitrobenzene was related positively with the initial inoculum amount. The maximum tolerance concentration of nitrobenzene for XY-1 was 800 mg/L. It could also degradate p-chloronitrobenzene and p-chloroaniline. The addition of Cu2+ and Cd2+ obviously inhibited the degradation of nitrbenzene for the strain, while Mg2+, Ca2+, Fe2+ had little effect on the degradation of nitrbenzene.The complete gene sequence of nbzA encoding nitrobenzene reducase was amplified with PCR from the strain XY-1, this sequence had 99% similarity to nbzA gene from other strains. XY-1 had bis-plasmid, a mutant strain with only one plasmid was obtained through plasmind-elimination, the mutant had the similar resistance to ampicillin, actinospectacin, chloromycetin, erythromycin, streptomycin, tetracycline and kanamycin with XY-1, but it wasn’t capable of degrading nitribenzene. We presumed that nbzA gene encoding nitrobenzene reducase may locat on one of the two plasmids for its lost from the mutant.Strain XY-1 was applied for the bioremediation of the nitrobenzene-contaminated soils under laboratory conditions. When concentration of aniline was at 60 mg/L, nitrobenzene could be degraded by the strain. The optimal temperature for the strain degrading nitrobenzene in soils was 30℃. When initial inoculation quantity was 106 CFU/g soils, with the water content in soils being 20%, the concentration of nitrobenzene in soils reduced to 1 mg/kg soils after 15 days treatment.