Mercury induced community tolerance in microbial biofilms is related to pollution gradients in a long-term polluted river

• The PICT of microbial communities in biofilms can be detected by the quantification of specific resistance genes.
• Amount of merA genes is correlated with the THg concentrations in the biofilms of polluted river.
• Efflux from WWTP and immigration of microorganisms from pristine environments influence on PICT development.

The net toxicity of different forms of mercury, in the long-term during their transformation processes, leads to the selection of resistant bacterial cells and this result in community tolerance which is pollution induced. Accordingly, based on profiles of a bacterial community structure, analysis of Hg resistant culturable bacteria and quantification of merA genes, we assessed development of pollution induced community tolerance in a mercury-polluted gradient in the Idrijca River. TTGE analysis did not show effects of mercury pollution to bacterial community diversity, while quantification of merA genes showed that merA genes can be correlated precisely (R2 = 0.83) with the total concentration of mercury in the biofilm microbial communities in the pollution gradient.