Bacterial communities of the Black Sea exhibit activity against persistent organic pollutants in the water column and sediments.

The ability of bacteria to degrade organic pollutants influences their fate in the environment, impact on the other biota and accumulation in the food web. The aim of this study was to evaluate abundance and expression activity of the catabolic genes targeting widespread pollutants, such as polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and hexachloro-cyclohexane (HCH) in the Black Sea water column and sediments. Concentrations of PAHs, PCBs and HCH were determined by gas chromatography (GC) coupled to mass spectrometry (MS) and electron capture (ECD) detectors. bphA1, PAH-RHDα, nahAc, linA and linB that encode biphenyl 2,3 dioxygenase, α-subunits of ring hydroxylating dioxygenases, naphthalene dioxygenase, dehydrochlorinase and halidohydrolase correspondently were quantified by quantitative PCR. More recalcitrant PAHs, PCBs and HCH tended to accumulate in the Black Sea environments. In water samples, 3- and 4-ringed PAHs outnumbered naphthalene, while PAHs with > 4 rings prevailed in the sediments. Congeners with 4-8 chlorines with ortho-position of the substituents were the most abundant among the PCBs. β-HCH was determined at highest concentration in water samples, and total amount of HCH exceeded its legacy Environmental Quality Standard value. bphA1, was the most numerous gene in water layers (10 ⁵ copies/mL) and sediments (10 ⁵ copies/mg), followed by linB and PAH-RHDα genes (10 ³ copies/mL; 10 ⁵ copies/mg). The least abundant genes were linA (10 ³ copies/mL; 10 ⁴ copies/mg) and nahAc (10 ² copies/mL; 10 ⁴ copies/mg). The most widely distributed gene bphА1 was one of the least expressed (10 ^-3 -10 ^-2 copies/mL; 10 ^-1 copies/mg). The most actively expressed genes were linB (10 ¹ -10 ² copies/mL; 10 ³ copies/mg), PAH-RHDα (10 ¹ copies/mL; 10 ² copies/mg) and linA (10 ^-1 -10 ⁰ copies/mL; 10 ⁰ copies/mg). Interaction of bacteria with PAHs, PCBs and HCH is evidenced by high copy numbers of the catabolic genes that initiate their degradation. More persistent compounds, such as high-molecular weight PAHs or β-HCH are accumulating in the Black Sea water and sediments, albeit microbial activity is directed against them.
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