Isolation and characterization of mercury-resistant bacteria from wastewater sources in Egypt

An important microbial resistance mechanism to mercury is its reduction into elemental mercury (facilitated by the merA gene). Thirty eight microbial isolates from a variety of wastewater sources in Egypt were collected. Approximately 14 of these isolates exhibited not only a high degree of tolerance to mercury (up to 160 ppm), but also a high resistance to other tested heavy metals. From them, the 10 most resistant isolates were selected for further study and were found to include 9 Gram-negative and 1 Gram-positive bacterial strains. Multi antibiotic resistance profiles were recorded for 6 out of the 10 selected isolates. All the tested Gram-negative isolates (n=9) harbored a plasmid-encoded merA gene. The mercury removal effectiveness for the 10 selected isolates ranged between 50-99.9%, among which Stenotrophomonas maltophilia ADW10 recorded the highest rate (99.9%; at an initial mercury concentration of 20 ppm). To the best of our knowledge, this is the first study to: (i) demonstrate the presence of multi metal resistant S. maltophilia bacterium with a high Hg tolerance capacity that would make it a suitable candidate for future bioremediation efforts in heavy metal polluted areas in Egypt; and (ii) report Pseudomonas otitidis as one of the MRB.

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