Microbial bioremediation of Cr(VI)-contaminated soil for sustainable agriculture

Rapid industrialization and anthropogenic activities have produced a huge amount of noxious Cr(VI), which accumulates in the soil for a longer period. As a consequence, that decreases rice plant productivity in chromium-contaminated agricultural fields of Sukinda mining area, Odisha. In this context, efforts are being made for microbial bioremediation of Cr(VI) in chromium-contaminated sites to maintain the soil healthy. Microbes with a high degree of Cr(VI) resistance have immense potential to acclimatize in adverse conditions with genetic modifications or alterations and are the potential candidate for Cr(VI) detoxification. Several species of Bacillus, Staphylococcus, Micrococcus Acinetobacter, Cellulomonas, Escherichia, Serratia, Pantoea, Pseudomonas, Achromobacter, and Ochrobactrum have been reported to reduce toxic Cr(VI) to less toxic Cr(III). As per our case study, the native bacterial strain Enterobacter cloacae CTWI-06 depicted high Cr(VI) resistance up to 3500 ppm and a wide array of other metals. In addition, the bacterial strain also showed various plant growth-promoting traits such as N2 fixation; phosphate (146.87 ppm), potassium (12.55 ppm), and zinc solubilization; and ammonification and indole-3-acetic acid production (114 μg mL−1). Under optimized conditions, the multimetal-resistant bacteria reduced 94% Cr(VI) within 92 h, as confirmed by FTIR and XRD analysis, and hence being validated as a potential bio-agent for bioremediation in multiple metal-contaminated sites. In conclusion, E. cloacae CTWI-06 strains have significant Cr(VI) bioremediation ability as well as plant growth-promoting characteristics in pot culture with reference to rice (Oryza sativa) cultivation. As the bacterial strains have the capability to survive under unfavorable conditions, efficiently reducing Cr(VI), and significantly promoting plant growth, that may be utilized for long-term bioremediation of Cr(VI) in chromium-contaminated soil as well as to maintain soil health for sustainable agriculture.