Recently, a team led by Dr. Xu Meiying, a researcher at the Institute of Microbiology of the Guangdong Academy of Sciences, has made new progress in the treatment of selenous acid pollution and the recovery of selenium resources. They discovered multiple strains of selenite-tolerant and highly efficient selenium-reducing bacteria. The related findings were published in the "Journal of Hazardous Materials."
Selenium is an essential trace element for the human body. However, the concentration difference between selenium deficiency and selenium toxicity in the human diet is very small. Residents in selenium-polluted areas may ingest excessive selenium from the environment through food absorption, air inhalation, and skin contact, leading to serious health problems such as blindness, hair loss, respiratory failure, and myocardial necrosis. In nature, selenite is the most toxic and common form of selenium. Reducing it to non-toxic, insoluble elemental selenium is an effective strategy for remediation of selenium pollution and recovery of valuable selenium resources. The recovered elemental selenium nanoparticles are widely used in industrial production due to their special photoelectric, semiconductor, and X-ray sensing properties.
Moreover, biologically synthesized elemental selenium nanoparticles exhibit significant antibacterial, antioxidant, and anticancer activities, with wide applications in medicine. However, currently reported selenium-reducing bacteria generally have low tolerance and reduction efficiency towards selenite, making it difficult to apply them in the remediation of selenite-polluted environments and industrial production of nano-selenium. To address this challenge, researchers isolated multiple functional bacterial strains with high tolerance and efficient reduction of selenite from the soil of the Enshi selenium mining area in Hubei Province. Among them, Oceanobacillus sp. ES111 showed the highest tolerance to selenite, with a tolerance concentration exceeding 700 mM, while Metasolibacillus sp. ES129 exhibited the highest reduction efficiency towards selenite, requiring only 24 hours to reduce 91% of selenite at a concentration of 1.22 mM.
Ultrastructural analysis revealed that strains ES111 and ES129 reduced selenite to Se0 in the cytoplasm, where small Se0 seeds aggregated to form larger elemental selenium nanoparticles through the Ostwald ripening process. Subsequently, the elemental selenium nanoparticles were released into the extracellular space through cell lysis. Transcriptome analysis indicated that the reduction of selenite may be mediated through various pathways, including low molecular weight thiols, thioredoxin/thioredoxin reductase systems, and pyruvate dehydrogenase. Upregulation of nucleotide excision repair and antioxidant enzyme-related gene expression may be the mechanism by which bacteria develop tolerance to selenite toxicity and maintain intracellular homeostasis.
This study identified multiple strains of selenite-tolerant and highly efficient selenium-reducing bacteria and investigated the kinetics of selenite reduction, the characteristics of nano-selenium products, and the mechanisms of biological selenium reduction and tolerance. It provides valuable microbial resources and scientific theoretical references for the treatment of high-concentration selenite pollution and the utilization of selenium resources.
Related paper information: https://doi.org/10.1016/j.jhazmat.2024.134491
