MerP/MerT-mediated mechanism: A different approach to mercury resistance and bioaccumulation by marine bacteria.

Currently, mechanism underlying mercury resistance and bioaccumulation of marine bacteria remains little understood. A marine bacterium Pseudomonas pseudoalcaligenes S1 is resistant to 120 mg/L Hg with bioaccumulation capacity of 133.33 mg/g. Accordingly, Hg resistance and bioaccumulation mechanism of S1 was investigated at molecular and cellular level. Annotation of S1 transcriptome reveals 772 differentially expressed genes, including Hg-relevant genes merT, merP and merA. Both merT and merP gene have three complete copies in S1 genome, while merA gene has only one. In order to evaluate the function of these Hg-relevant genes, three recombinant strains were constructed to express MerA (named as A), MerT/MerP (TP) and MerT/MerP/MerA (TPA), respectively. The results show that Hg resistance of strain TP, TPA, and A are improved with minimum inhibition concentration (MIC) being 60 mg/L, 40 mg/L, and 20 mg/L, respectively compared to 2 mg/L of host strain. Strain TP and TPA exhibit enhanced Hg bioaccumulation capacity, while strain A does not differ from the control. Their equilibrium Hg bioaccumulation capacities are 110.48 mg/g, 94.49 mg/g, 83.76 mg/g and 82.29 mg/g, respectively. Summarily, different from most microorganisms that exhibit Hg resistance by MerA-mediated mechanism, marine bacterium S1 achieves Hg resistance and bioaccumulation capability via MerT/MerP-mediated strategy.