Is the merA gene sufficient as a molecular marker of mercury bacterial resistance?

Gene encoding mercuric ion reductase, merA is a crucial component of the mer operon for reduction of nonorganic mercury ions into less toxic form. The merA gene or its fragments are commonly used as a molecular marker of bacterial resistance to mercury. In this study, it was tested whether the merA gene can be considered as a molecular marker of mercury bacterial resistance. For this purpose, the presence of the mer operon in bacteria isolated from the microbiota of Tussilago farfara L. growing in post-industrial mercury-contaminated and non-contaminated areas was verified by merA gene identification. Mercury resistance was determined by analyzing the bacterial growth parameters in standard Luria-Bertani (LB) medium with mercury concentration of 0.01% (w/v) and in medium without mercury addition. The results obtained showed that the merA gene was present in all T. farfara L. bacterial isolates growing in both mercury-contaminated and noncontaminated soils, however, only the isolates from mercury-contaminated areas were able to grow under mercury conditions. Although merA is commonly regarded as a molecular marker of bacterial mercury resistance, results of our research indicate the need for a verification of that statement/thesis and further investigation of bacterial mercury resistance to indicate other its key markers, structures, or mechanisms.