Cr(VI) Removal by Recombinant Escherichia coli Harboring the Main Functional Genes of Sporosarcina saromensis M52

Exploration of risk analysis and elimination methods for a Cr(VI)-removal recombinant strain through a biosafety assessment in mice

Though recombinant strains are increasingly recognized for their potential in heavy metal remediation, few studies have evaluated their safety. Moreover, biosafety assessments of fecal-oral pathway exposure at country as well as global level have seldom analyzed the health risks of exposure to microorganisms from a microscopic perspective. The present study aimed to predict the long-term toxic effects of recombinant strains by conducting a subacute toxicity test on the chromium-removal recombinant strain 3458 and analyzing the gut microbiome. The available disinfection methods were also evaluated. The results showed that strain 3458 induced liver damage and affected renal function and lipid metabolism at 1.0 × 1011 CFU/mL, which may be induced by its carrier strain, pET-28a. Strain 3458 poses the risk of increasing the number of pathogenic bacteria under prolonged exposure. When 500 mg L-1 chlorine-containing disinfectant or 250 mg L-1 chlorine dioxide disinfectant was added for 30 min, the sterilization rate exceeded 99.9 %. These findings suggest that existing wastewater disinfection methods can effectively sterilize strain 3458, ensuring its application value. The present study can serve a reference for the biosafety evaluation of the recombinant strain through exposure to the digestive tract and its feasibility for application in environmental pollution remediation.

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 of tannery effluent, and its accumulation in soil and water causes severe environmental concerns of increasing public health issues. The present study focus 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 Pseudomonas putida and transferred to E. coli DH5α 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 DH5α were grown in chromium supplemented media revealed significant growth, but strains cured type Pseudomonas putida and E. coli DH5α were minimum growth. The Cr(VI) reduction employed by transformant E. coli DH5α and wild Pseudomonas putida was 42.52 ± 1.48% and 44.46 ± 0.55%, respectively. The culture supernatant of the wild Pseudomonas putida and transformant E. coli DH5α showed an increased reduction of Cr(VI) compared to cell extract supernatant and cell debris due to the extracellular activity of chromium reductase has been responsible for Cr(VI) reduction. Besides, the chromium reductase gene was confirmed in the isolated Pseudomonas putida and transformant E. coli DH5α.

CONCLUSIONS

Transformant bacteria could employ an alternative method for heavy metal detoxification in contaminated environments like tannery effluent and mining processes.