Environmentally relevant parameters affecting PCB degradation: carbon source- and growth phase-mitigated effects of the expression of the biphenyl pathway and associated genes in Burkholderia xenovorans LB400

Abstract

The principal means for microbial degradation of polychlorinated biphenyls (PCBs) is through the biphenyl pathway. Although molecular aspects of the regulation of the biphenyl pathway have been studied, information on environmental facets such as the effect of alternative carbon sources on (polychlorinated) biphenyl degradation is limited. Here we explore the effect of environmental conditions (e.g., carbon source and growth phase) on the variation in PCB degradation profiles of Burkholderia xenovorans LB400. Genome-wide expression patterns reveal 25 genes commonly up-regulated during PCB degradation and growth on biphenyl to be upregulated in the transition to stationary phase (relative to growth on succinate) including two putative detoxification pathways. Quantitative reverse transcription PCR (Q-RT-PCR) analysis of the upper biphenyl pathway (bphA, bphD, and bphR1), and detoxification genes in response to environmental conditions suggest associated regulation of the biphenyl pathway and chloroacetaldehyde dehydrogenase. The response of genes in the upper biphenyl pathway to carbon source competition and growth phase reveals inhibition of the biphenyl pathway by PCBs. Although PCBs are not degraded during growth on succinate with PCBs, expression data indicate that the biphenyl pathway is induced, suggesting that post-transcriptional regulation or active transport of biphenyl maybe limiting PCB degradation. Identification of the involvement of peripheral pathways in degradation of PCBs is crucial to understanding PCB degradation in an environmental context as bacteria capable of biodegradation experience a range of carbon sources and growth phases.