denitirification
Most studies of bacterial denitrification have used nitrate (NO3) as the first electron acceptor, whereas relatively less is understood about nitrite (NO2) denitrification. We isolated novel bacteria that proliferated in the presence of high levels of NO2 (72 mM). Strain YD50.2, among several isolates, was taxonomically positioned within the subclass of Proteobacteria and identified as Ochrobactrum anthropi YD50.2. This strain denitrified NO2 as well as NO3. The gene clusters for denitrification (nar, nir, nor, and nos) were cloned from O. anthropi YD50.2, in which the nir and nor operons were linked. We confirmed that nirK in the nir-nor operon produced a functional NO2 rductase containing copper that was involved in bacterial NO2 reduction. The strain denitrified up to 40 mM NO2 to dinitrogen under anaerobic conditions in which other denitrifiers or NO3 reducers such as Pseudomonas aeruginosa and Ralstonia eutropha and nitrate-respiring Escherichia coli neither proliferated nor reduced NO2. Under nondenitrifying aerobic conditions, O. anthropi YD50.2 and its type strain ATCC 49188T proliferated even in the presence of higher levels of NO2 (100 mM), and both were considerably more resistant to acidic NO2 than were the other strains noted above. These results indicated that O. anthropi YD50.2 is a novel denitrifier that has evolved reactive nitrogen oxide tolerance mechanisms.
American Society for Microbiology
