Isolation of a naturally-occurring nickel resistance plasmid from a rare hypersaline estuary (Laguna Madre,Texas, USA) for potential use as a bio-indicator of metal contamination |
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Authors: | Molina Tiffany L Patel Roshni Molina Daren D Persans Michael W Lowe Kristine L |
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Institution: | (1) Department of Biology, University of Texas—Pan American, 1201 W. University Drive, Edinburg, TX 78539, USA; |
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Abstract: | Metal-resistant bacteria were isolated from sediments of the Laguna Madre, a rare hypersaline estuary impacted by many anthropogenic
compounds, including various metals and metalloids. Bacteria were initially isolated on nutrient agar supplemented with NaCl;
random isolates (n = 100) were tested for metal resistance toward zinc, nickel, chromium, and cadmium using a pour plate disc assay. Metal-resistant
cultures were assayed for plasmids that contained naturally-occurring heavy metal resistance genes. Putative metal-resistance
plasmids were tested for metal-resistance efficacy by transforming a metal-sensitive strain of Escherichia coli. Polymerase Chain Reaction (PCR) primers were designed to detect cnrA, part of a nickel–cobalt resistance gene cluster, and restriction endonuclease digests were performed to detect restriction
sites within the plasmid. Results showed that many bacterial isolates tested were resistant toward most of the metals used
in this study. Among tested bacteria cultures, 34 were resistant to zinc, 64 were resistant to chromium, and 51 resistant
to cadmium. Only 8 cultures were resistant to nickel; however, most bacteria were found to be resistant to more than one metal.
Several plasmids were found from the bacteria isolates. One plasmid, designated pDZ5, was isolated from a bacterium identified
as Bacillus pumilus by 16S rRNA sequencing. Plasmid pDZ5 conferred nickel resistance to the metal-sensitive E. coli strain and was found to contain cnrA as confirmed by PCR amplification. Plasmid pDZ5 was successfully cut with restriction enzymes for potential ligation with
reporter genes. The presence, abundance and expression of pDZ5 may prove to be a useful bio-indicator of metal contamination,
specifically nickel pollution, in the Laguna Madre due to the fewer number of bacteria that were nickel-resistant compared
to other metals. |
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