3 years ago

Multiple roles of two efflux pumps in a polycyclic aromatic hydrocarbon-degrading Pseudomonas putida strain B6-2 (DSM 28064).

Hongzhi Tang, Kunzhi Zhang, Ping Xu, Fei Tao, Xuemei Yao
Microbial bioremediation is a promising approach for the removal of polycyclic aromatic hydrocarbon (PAH) contaminants. Many degraders of PAHs possess efflux pump genes in their genomes; however, their specific roles in the degradation of PAHs have not been clearly elucidated. In this study, two efflux pumps, TtgABC and SrpABC, were systematically investigated to determine their functions in a PAH-degrading Pseudomonas putida strain B6-2 (DSM 28064). The disruption of genes ttgABC or srpABC resulted in a defect in organic solvent tolerance. TtgABC was found to contribute to antibiotic resistance; SrpABC only contributed to antibiotic resistance under an artificial overproduced condition. Moreover, a mutant strain without srpABC did not maintain its activity in long-term biphenyl (BP) degradation, which correlated with the loss of cell viability. The expression of SrpABC was significantly upregulated in the course of BP degradation. BP, 2-hydroxybiphenyl, 3-hydroxybiphenyl, and 2,3-dihydroxybiphenyl (2,3-DHBP) were revealed to be the inducers of srpABC 2,3-DHBP was verified to be a substrate of pump SrpABC; SrpABC can enhance the tolerance to 2,3-DHBP by pumping it out. The mutant strain B6-2ΔsrpS prolonged BP degradation with the increase of srpABC expression. These results suggest that the pump SrpABC of strain B6-2 plays a positive role in BP biodegradation by pumping out metabolized toxic substances such as 2,3-DHBP. This study provides insights into the versatile physiological functions of the widely distributed efflux pumps in the biodegradation of PAHs.IMPORTANCE PAHs are notorious for their recalcitrance to degradation in environment. The high frequency of the occurrence of the efflux pump genes was observed in the genomes of effective PAH-degraders; however, their specific roles in the degradation of PAHs are still obscure. The significance of our study is identifying the function and mechanism of the efflux pump SrpABC of Pseudomonas putida strain B6-2 (DSM 28064) in the biphenyl degradation process. SrpABC is crucial in releasing the toxicity caused by intermediates that are unavoidably produced in PAH degradation, which will allow an understanding on how cells maintain the intracellular balance of materials. It is reasonable to suggest that this study will provide a new perspective on the PAH recalcitrance, and will shed light on enhancing the PAH degradation by genetic engineering.

Publisher URL: http://doi.org/10.1128/AEM.01882-17

DOI: 10.1128/AEM.01882-17

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