Genes Related to Chromate Toxicity Challenging Systems in Native Staphylococci Species Isolated from a Fly Ash Dumping Site

Abstract

Staphylococci species resistant to chromate were isolated from a chromate polluted fly ash dumping site. The mechanisms used by these gram positive bacteria to survive high levels of chromate in this environment were studied. Using PCR amplification and computer assisted analyses, the existence of gene clusters that are associated to chromate challenging systems in the genome of staphylococcal strains was studied. A DNA fragment was amplified and was shown to be part of a gene encoding protein sequence with the highest homologies to ABC transporter ATP binding protein in S. saprophyticus (YP_300821.1) and S. aureus genomes (ADI98643.1). This ABC transporter is a P-loop NTPase homologous to similar P-loop ABC sulfate transporters Arth_0806 (YP_830304.1), Arth_857 (gi116609531), and Arth_858 (gi116609532) that were abundantly expressed in Arthrobacter sp. during chromate stress. When the full gene encoding this ABC transporter was cloned into a pGEMT vector and transferred to Escherichia coli, the transformed E. coli cells could grow on a medium supplemented with chromate, showing that this ABC transporter conferred resistance to chromate. Another fragment was part of a gene that encoded a nirD Rieske domain protein in S. epidermidis ZP_04817633 and S. aureus NP_647138. The nirD from the Staphylococci had homologies with Arth_3714 YP_833189.1, a Rieske (2Fe-2S) domain protein abundantly up-regulated in Arthrobacter sp. during chromate stress. A third fragment was part of a gene that encoded proteins homologous to chromosome segregation SMC proteins YP_301625.1, EGS78669.1, and ZP_04866016.1 respectively in the genomes of S. saprophyticus, S. epidermidis, and S. aureus. Phylogenetic analyses showed that the SMC protein was homologous to So3429 gi24349654, a RecX protein that was shown to be involved in DNA damage repair in Shewanella oneidensis in response to chromate stress. This study reports that the staphylococcal strains isolated from the chromate polluted fly ash dumping site harbored genes that might be used by these organisms to survive chromate toxicity.

Keywords:

• chromate-resistant Staphylococci
• fly ash dumping site
• chromate challenging systems

Acknowledgments

The authors are grateful to the Institute of Microbial Biotechnology and Metagenomics (IMBM), Department of Biotechnology, University of Western Cape and its Director Professor Don Conwan for hosting Ms. Kouadjo for her PhD scholarship.