Biodegradation of 2-chlorobenzoic acid by recombinant Burkholderia cepacia under hypoxic conditions

Laboratory experiments using batch shake flasks, continuous flow chemostat reactors, and membrane bioreactor (MBR) systems were conducted to investigate the cometabolic biodegradation of 2-chlorobenzoic acid (2-CBA), a model recalcitrant chlorinated organic compound, by untransformed and recombinant Burkholderia cepacia strain DNT under hypoxic conditions.; The recombinant B. cepacia cells containing bacterial hemoglobin (VHb) gene, vgb, have an advantage over untransformed cells in terms of 2-CBA degradation and growth rate under hypoxic conditions using acetate as the primary carbon source. The improvement in 2-CBA degradation correlated with higher oxygen uptake rate found in the recombinant B. cepacia cells compared to the untransformed cells. The vgb-containing recombinant B. cepacia grown in continuous flow chemostat systems and MBR systems not only degraded 2-CBA better, but also the corresponding chloride release to 2-CBA degraded ratio was nearly stoichiometric under hypoxic conditions. The chloride release to 2-CBA degraded ratio is indicative of complete degradation of 2-CBA rather than to intermediates containing chloride. This effect was seen in the recombinant cells over a range of 2-CBA concentrations (0.5–2mM) and acetate (10–20 mM). The plasmid containing vgb in the recombinant B. cepacia was stable in all systems, and the stability was higher under hypoxic conditions.; This bacterial hemoglobin technology was further successfully demonstrated in MBR systems over a range of loading and operating conditions; simulating a bioreactor with high biomass concentration, hypoxic conditions, and complete retention of cells in the bioreactor. The research showed that use of recombinant bacterial hemoglobin technology is a feasible option for full scale enhanced bioremediation of water contaminated by chlorinated organics in a MBR system.