Bioremediation of hexavalent chromium by transformation of Escherichia coli DH5α with chromate reductase (ChrR) genes of Pseudomonas putida isolated from tannery effluent

Aims Hexavalent chromium (Cr(VI)), a toxic heavy metal, is a serious pollutant from tannery effluent, and its accumulation in soil and water causes severe environmental concerns and increasing public health issues. The present study focuses on the isolation and identification of chromium-reducing bacteria collected from the tannery industry in Dindigul, Tamil Nadu. Chromium-reducing bacteria Pseudomonas putida were identified by 16S rRNA sequencing followed by BLAST search. The plasmid with Cr(VI) reductase gene was isolated from Ps. putida and transferred to Escherichia coli DH5 alpha for further studies. Methods and Results The bacterial cultures were kept under controlled conditions for 72 h to observe the growth rates and bacterial resistance to chromium. When strains wild-type and transformant E. coli DH5 alpha were grown in chromium-supplemented media, they revealed significant growth, but strains cured type Ps. putida and E. coli DH5 alpha recorded minimum growth. The Cr(VI) reduction employed by transformant E. coli DH5 alpha and wild Ps. putida was 42.52 +/- 1.48% and 44.46 +/- 0.55%, respectively. The culture supernatant of the wild Ps. putida and transformant E. coli DH5 alpha showed an increased reduction of Cr(VI) compared with cell extract supernatant and cell debris due to the extracellular activity of chromium reductase being responsible for Cr(VI) reduction. Besides, the chromium reductase gene was confirmed in the isolated Ps. putida and transformant E. coli DH5 alpha. Conclusions Transformant bacteria could employ an alternative method for heavy metal detoxification in contaminated environments like tannery effluent and mining processes. Significance and Impact of Study High Cr(VI) concentration resistance and high Cr(VI) reducing the strain's ability make it suitable for bioremediation. These possible horizontal gene transfer events indicated in this study may have enabled transformant E. coli DH5 alpha as a good candidate for reducing the heavy metal pollution.

Automated summary

This study focused on the isolation and identification of chromium-reducing bacteria from tannery effluent. Pseudomonas putida was identified as a potential strain for chromium reduction, and its reductase gene was transferred to Escherichia coli DH5 alpha for further study. The results showed that the transformant strain had a high ability to reduce hexavalent chromium, indicating its potential for bioremediation.