Functional efficiency of MerA protein among diverse mercury resistant bacteria for efficient use in bioremediation of inorganic mercury

MerA protein of mer operon in mercury resistant bacteria influences transformation of Hg²⁺ to Hg⁰. Both in-silico and in-vivo studies have been carried out and MerA sequences, conserved motifs for mercury binding and NADPH (GCVPSK and LSCCA) varied widely in both Gram-positive and Gram-negative bacteria. As MerA-NADPH-FAD complex plays an important role in mercury volatilization, molecular interaction studies between MerA, NADPH, FAD and Hg²⁺ was carried out to study the efficiency of transformation of Hg²⁺ to Hg⁰ in mercury resistant bacteria. After the prediction of suitable models and molecular interaction analysis, the potential energies in the selected bacteria were as follows: Bacillus thuringiensis (NADPH: -5.15 kcal/mol and FAD: -9.63 kcal/mol), Pseudomonas aeruginosa (NADPH: -3.8 kcal/mol and FAD: -8.56 kcal/mol), Exiguobacterium sp. (NADPH: -3.37 kcal/mol and FAD: -8.42 kcal/mol), Vibrio sp. (NADPH: -3.3 kcal/mol and FAD: -6.7 kcal/mol) and Escherichia coli (NADPH: -3.28 kcal/mol and FAD: -5.69 kcal/mol). Additionally, the binding scores between MerA and Hg²⁺ followed the similar trend and found higher in B. thuringiensis (3.79) followed by P. aeruginosa (3.57), Exiguobacterium sp. (2.37), Vibrio sp. (1.47) and E. coli (1.07). ANOVA (2-way) result showed the significant (P < 0.05) variation among the energy values obtained after interaction studies. In-vivo analysis of expression of merA gene and Hg²⁺ removal efficiency also followed the same pattern with a highly significant correlation (P < 0.001) between the binding energy, binding score and expression pattern of merA gene as well as Hg²⁺ volatilization. Thus, the mercury removal efficiency of bacteria is genera specific which is correlated with the binding efficiency between MerA-NADPH complex and Hg²⁺ in mer operon mediated mercury resistant bacteria.