Effects of chlorobenzoate transformation on the Pseudomonas testosteroni biphenyl and chlorobiphenyl degradation pathway

Abstract

Bacterial conversion of biphenyl (BP) and chlorobiphenyls (CBPs) to benzoates and chlorobenzoates (CBAs) proceeds by introduction of molecular oxygen at the 2,3 position, followed by a 1,2-meta cleavage of the molecule. Complete mineralization of CBPs requires the presence of two sets of genes, one for the transformation of CBPs into CBAs and a second for the degradation of CBAs. It has been shown previously that removal of the CBAs produced from the degradation of CBPs is essential for efficient degradation of CBPs. In this study we confirmed that CBAs inhibit BP and CBP transformation in Pseudomonas testosteroni B-356. Among the three monochlorobenzoates tested, 3-chlorobenzoate was the most effective inhibitor. Furthermore, we found that in strain B-356, CBA transformation is controlled by BP-induced oxygenases that are not present in benzoate-grown cells. We found that this BP-linked CBA transformation pathway transformed CBAs produced from CBPs into several metabolites, including chlorocatechols and corresponding muconic semialdehydes. These metabolites inhibited the 2,3-dihydroxybiphenyl 1,2-dioxygenase, while CBAs by themselves had no effect on this enzyme. Therefore, on the basis of this and other observations, it appears that when CBAs produced from CBPs accumulate in the growth medium, they are converted into unproductive metabolites that reduce the flux of the BP and CBP degradation pathway. The practical implications of these interactions on the microbial degradation of polychlorinated BPs are also discussed.

Evidence of aerobic utilization of di‐ortho‐substituted trichlorobiphenyls as growth substrates by Pseudomonas sp. SA‐6 and Ralstonia sp. SA‐4

“…Although this is not a feature commonly encountered in biphenyl degraders, such phenomena have been reported for Burkholderia sp. LB400 (Bedard and Haberl, 1990) and Pseudomonas testosteroni B-356 (Sondossi et al, 1992). Incomplete degradation of PCBs to CBA products is not unusual and the formation of other intermediates has also been reported in the experiments of other researchers (Fava and Marchetti, 1991;Arensdorf and Focht, 1994;Bruhlmann and Chen, 1999).…”

Catabolic pathways and cellular responses of Pseudomonas putida P8 during growth on benzoate with a proteomics approach

“…This was attributed to the flux limitation of the ortho-cleavage pathway and the overflow of metabolites within the pathway. That two different metabolic pathways could be initiated for benzoate, so Sondossi et al (1992) unique to P8 has never been reported in other P. putida strains. In recent years, proteome analysis has been successfully utilized to elucidate the degradation pathways for aromatic compounds, including the catabolic pathways for benzoate.…”

Prospects for using combined engineered bacterial enzymes and plant systems to rhizoremediate polychlorinated biphenyls

“…Later, DoxG variants exhibiting higher ability to cleave 3,4-dihydroxybiphenyl metabolites were obtained by directed evolution (Fortin et al, 2005), showing the feasibility of engineering extradiol dioxygenases to expand the range of PCB substrates metabolized by the biphenyl pathway. A second limitation of the 2,3-DHBD is its high sensitivity to 3-chlorocatechol which was shown to interfere with PCB metabolism (Sondossi et al, 1992). However, the catecholic inhibition of 2,3-DHBD does not restrict PCB degradation in engineered bacteria that can degrade chlorobenzoates efficiently (Saavedra et al, 2010).…”