Modified dehydrogenase enzyme assay for evaluation of the influence of Hg, Cd, and Zn on the bacterial community structure of a wastewater treatment plant

Abstract

In this study, a traditional assay was modified to evaluate the effect of Hg, Cd, and Zn on the bacterial community of a sequencing batch reactor and activated sludge plants and heavy metal-resistant bacterial species were determined. After the isolation of metal-resistant bacteria, their 16S rRNA gene fragments were sequenced. The BLAST program was used to compare the resulting 16S rRNA sequences with those in GenBank database to identify the isolated bacterial species. Hg was found to be the most toxic metal for both bacterial communities investigated. Sequence batch reactor bacteria were comparatively more resistant to Hg, Cd, and Zn than those from activated sludge. The resistant strains were close to the members of genus Pseudomonas, Kocuria, Stenotrophomonas, Enterococcus, and Staphylococcus. The modified dehydrogenase enzyme assay seems to be simple, robust, and competent for evaluation of the impact of metals on bacterial activity. Sequencing batch reactor systems should be preferred over activated sludge when wastewaters containing hazardous metals are to be treated.

Keywords:

• metal toxicity
• dehydrogenase enzyme assay
• sequencing batch reactor
• activated sludge

Acknowledgments

This work was supported by the Department of Environmental Health Engineering, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors would like to thank the Environment Research Center at the Isfahan University of Medical Sciences, Isfahan, Iran, for funding support [number 114-2] during the preparation of this manuscript.