Benzopyrene biodegradation by multiple and individual mesophilic bacteria in axenic conditions and in soil samples

Thus far, only a handful of bacterial strains that can independently degrade and utilize benzo[a]pyrene (BaP) as the sole carbon source have been isolated and characterized. Here, three new bacterial strains, JBZ1A, JBZ2B, and JBZ5E, were isolated from contaminated soil and, using 16S rRNA sequencing, were identified as Bradyrhizobium japonicum, Micrococcus luteus, and Bacillus cereus, respectively. The growth ability of each individual strain and a consortium of all strains in the presence of BaP (4-400 {micro}mol{middle dot}l-1, pH 7, 37{degrees}C) was identified by the doubling time (dt). The results illustrated that dt decreased with increasing BaP concentrations for individual strain and the consortium. The optimum growth conditions of the consortium were 37{degrees}C, 0.5% NaCl (w/v), and pH 7. Under these conditions, the degradation rate was 1.06 {micro}mol{middle dot}l-1{middle dot}day-1, whereas that of individual strains ranged 0.9-0.38 {micro}mol{middle dot}l-1{middle dot}day-1. B. cereus had the strongest contribution to the consortiums activity, with a degradation rate of 0.9 {micro}mol{middle dot}l-1{middle dot}day-1. The consortium could also remove BaP spiked with soil, but at a lower rate (0.01 {micro}mol.l-1.day-1). High-performance liquid chromatography-high-resolution tandem mass spectrometry permitted the detection of the metabolites of these strains, and a biodegradation pathway has been proposed.