Biological treatment of hazardous heavy metals by Streptomyces rochei ANH for sustainable water management in agriculture

Microbial bioremediation of heavy metals-polluted industrial effluents has been adopted as one of the most effective eco-friendly tool to cope up with the harmful effects of metals. This study was designed to investigate the biosorption potential of marine actinomycetes isolated from the Alexandrian Mediterranean Seacoast, Egypt, with their potential use in metal remediation of industrial effluents. Among the nine marine actinomycetes isolates, Streptomyces rochei ANH showed the highest versatile metal resistance capability with MIC values of 125 mg/l for Cr6+ and 60 mg/l for both Cd2+ and Pb2+. Additionally, scanning electron micrographs showed complete disintegration of Cr6+-treated biomass compared with the control ones where spores remained intact and connected in long chains. The study also aimed to improve the percentage of Cr6+ biosorption by S. rochei ANH biomass using the statistical designs of Plackett–Burman and Box-Behnken where up to 85% of Cr6+ removal was recorded under the following conditions: pH (5), incubation temperature (30 °C), contact time (3 h), agitation speed (90 rpm), initial Cr6+ concentration (50 mg/l) and living biomass concentration (10 mg/ml). The results also showed that the percentage of Cr6+ biosorption by S. rochei ANH decreased gradually beyond these values. Moreover, the results revealed that the use of the biomass of S. rochei ANH is an effective biotechnological agent for the biological treatment of heavy metal-contaminated tannery effluent where the percentages of metal removal were in the following order: Ni2+ (100%) ≥ Cu2+  ≥ Mn2+  ≥ Fe2+  > Pb2+ (95%) ≥ Cd2+  > Cr6+ (86%). Furthermore, the treated effluent exhibited a stimulating effect on the germination process of Lepidium sativum seeds. Therefore, the present study implies that S. rochei ANH can be considered a powerful candidate to mitigate hazardous heavy metals pollution from industrial effluents and improve the water quality for agricultural purposes.