Roles of Pseudomonas aeruginosa and Ensifer adhaerens in accelerating nitrobenzene biodegradation by removing an inhibitory intermediate

Pseudomonas aeruginosa and Ensifer adhaerens were isolated from aerobic biomass acclimated to nitrobenzene (NB) based on ability to biodegrade NB and its intermediate, o-aminophenol. Bioaugmenting either of them into the acclimated biomass accelerated NB biodegradation. The NB removal rates were as 19% and 144% faster, respectively, with P. aeruginosa and E. adhaerens, compared to the acclimated biomass, even though the dry-weight concentrations of P. aeruginosa and E. adhaerens were only ∼10% of the acclimated biomass. Biodegradation was further accelerated by another 36%–217% when P. aeruginosa and E. adhaerens, respectively, were bioaugmented into the acclimated biomass at ∼10% of the dry weight. The primary benefit of P. aeruginosa and E. adhaerens came from their ability to biodegrade rapidly an inhibitory intermediate of NB biodegradation, o-aminophenol. Phylogenetic analysis showed that Thauera, which is known to be active in NB biodegradation, was by far the dominant genus in the acclimated biomass. Although the abundances of E. adhaerens and P. aeruginosa were minimal in the acclimated biomass (∼0.01%), they played an important role in accelerating NB biodegradation by bioaugmention once they were isolated, enriched, and bioaugmented.