Transformation of hydroxylated derivatives of 2,5-dichlorobiphenyl and 2,4,6-trichlorobiphenyl by Burkholderia xenovorans LB400

The polychlorinated biphenyl (PCB)-degrading bacterium, Burkholderia xenovorans LB400, was capable of transforming three hydroxylated derivatives of 2,5-dichlorobiphenyl (2,5-DCB) (2'-hydroxy- (2'-OH-), 3'-OH-, and 4'-OH-2,5-DCB) when biphenyl was used as the carbon source (i.e., biphenyl pathway-inducing condition), although only 2'-OH-2,5-DCB was transformed when the bacterium was growing on succinate (i.e., condition non-inductive of the biphenyl pathway). On the contrary, hydroyxlated derivatives of 2,4,6-trichlorobiphenyl (2,4,6-TCB) (2'-OH-, 3'-OH-, and 4'-OH-2,4,6-TCB) were not significantly transformed by B. xenovorans LB400, regardless of the carbon source used. Gene expression analyses showed a clear correlation between the transformation of OH-2,5-DCBs and expression of genes of the biphenyl pathway. The PCB metabolite, 2,5-dichlorobenzoic acid (2,5-DCBA), was produced following the transformation of OH-2,5-DCBs. 2,5-DCBA was not further transformed by B. xenovorans LB400. The present study is significant because it provides evidence that PCB-degrading bacteria are capable of transforming hydroxylated derivatives of PCBs, which are increasingly considered as a new class of environmental contaminants.

Structure elucidation and characterization of polychlorinated biphenyl carboxylic acids as major constituents of chromophoric dissolved organic matter in seawater

Chromophoric or colored dissolved organic matter (CDOM) is one of the principal light adsorbing components of seawater, particularly in the ultraviolet, where it attenuates over 90% of downwelling ultraviolet radiation. In highly productive coastal regions and throughout most of the global ocean, in situ biological production is the major source of CDOM. However, little is known about CDOM composition on the molecular level, and there are only a few reports that link CDOM composition to autochthonous biological sources. Here we report the isolation and characterization of CDOM components from one coastal and two open-ocean sites. Each sample contains a complex mixture of light absorbing (300-400 nm) components, including 2,4-dichlorobenzoic acid and a suite of novel, polychlorinated biphenyl carboxylic acids that closely resemble polychlorinated biphenyls (PCBs) of anthropogenic origin. However, the global inventory and isomer distribution of dissolved chlorinated aromatic acids suggest they are derived from in situ biological production rather than anthropogenic contaminants. These novel chlorinated aromatic acids account for a significant amount of CDOM adsorption in the ultraviolet.