Mercuric reductase gene (merA) activity in a mercury tolerant sulphate reducing bacterium isolated from the Kongsfjorden, Arctic

Abstract

The bacterial reduction of mercury is one of the transformation processes where ionic form (Hg2+) converts into elemental form (Hg0). The biological reduction of mercury is facilitated by the mercuric reductase (merA) gene. The significance of understanding the role of microbial mercury reduction in the Arctic during the changing climate conditions is high as it acts as the sink as well as a source of mercury. The present study was carried out to assess the prevalence of mercury tolerant bacteria and to know the distribution of merA in the Arctic bacterial communities. Citrobacter freundii strain MM7, a psychrotrophic, gram-negative, facultative anaerobic, non-traditional sulphate-reducing bacterium, isolated from the sediments of Kongsfjorden showed tolerance to mercury up to 10.0 mg/L in vitro. Mercury removal experiment confirmed the removal of ∼80% of mercury mediated by plasmid-borne merA gene. Studies using Fourier transform infrared (FTIR) showed the metabolic changes incited by mercury, and the spectroscopic differences reflected that the functional groups like alkynes, aromatic phosphates, organic phosphates, methyl, methylene, and amide groups present in the bacterial surface owe a significant part in Hg biosorption and removal. The present study provides insights on the mercury resistance in an Arctic bacterial strain and suggests the potential application of Citrobacter freundii strain MM7 in the bioremediation of mercury from the natural environment.