Enhanced kinetics of genetically engineered Burkholderia cepacia: Role of vgb in the hypoxic cometabolism of 2-CBA

Abstract

Application of Vitreoscilla hemoglobin (VHb) technology to 2-CBA degradation by Burkholderia cepacia strain DNT under hypoxic conditions was studied in continuous culture chemostats. Dechlorination abilities of both recombinant (VHb gene (vgb) containing) and untransformed cells were investigated at various dilution rates to ensure complete degradation of 2-CBA. As the dilution rate increased from 0.025 to 0.25 h-1, the ratios of chloride release to degraded 2-CBA concentration decreased from 0.95 to 0.72 and from 0.89 to 0.39 for recombinant and untransformed cells, respectively. A nonstoichiometric relationship between chloride release and 2-CBA degradation was more pronounced for untransformed cells. Recombinant cell densities were 0.1-0.2 g L-1 greater than untransformed cell densities for a range of dilution rates. As the dilution rate increased, the oxygen uptake rate (OUR) and the substrate utilization rate (SUR) decreased for both strains. The OUR/SUR ratio increased as the dilution rate increased for both strains but was much higher for the recombinant strain compared to untransformed cells. The specific 2-CBA degradation rate of recombinant cells was greater than that of untransformed cells (1.17 vs. 0.46 mg CBA (mg)-1 day-1, and half-saturation constants for recombinant cells were lower than those of untransformed cells (0.18 and 0.32 mg CBA L-1, respectively). The pseudo-first-order degradation constants, k1CBA and k1ACE, were higher for recombinant cells (6.5 L (mg cells)-1 day -1 and 95.6 L (mg cells)-1 day-1, respectively) than those of untransformed cells (1.44 L (mg cells)-1 day -1 and 73.7 L (mg cells)-1 day-1, respectively). © 2004 Wiley Periodicals, Inc.