Exploration on the mechanism of Cr(VI) bioreduction by a novel cold and salt tolerant bacteria Algoriphagus sp. CM16 isolated from marine sediment

Hexavalent chromium pollution, a hazardous heavy metal contamination, poses grave risks to human health, finding environmentally friendly ways to treat hexavalent chromium has become an urgent scientific problem. In this study, a novel marine hexavalent chromium-reducing strain, Algoriphagus sp. CM16 was discovered, the first report of a chromium-reducing bacterium of the genus Algoriphagus . CM16 exhibits exceptional reduction capacity at lower temperature (25°C) and higher salinity (3%), removing 85.3% of 50 mg/L chromium within 48 hours, unaffected by heavy metal ions and anions (NO 3 ²⁻, SO 4 ²⁻). Utilizing diverse carbon source and electron mediators, CM16 significantly accelerates Cr(VI) removal. Strain CM16 mainly reduces Cr(VI) to trivalent chromium in the cytoplasm and cell envelope and forming an amorphous precipitate while producing massive Catalase(CAT) and Superoxide Dismutase(SOD) to effectively protect the cells from oxidative damage caused by Reactive Oxygen Species(ROS) during the reduction process. Furthermore, the whole-genome sequencing analysis suggested that CM16's robust chromium reduction capabilities and elevated levels of antioxidant enzymes may stem from a long-term adaptation strategy to harsh polar environments. Due to high chromium reduction efficiency, high salt tolerance properties, and high content of antioxidant enzymes, Algoriphagus sp. CM16 is predicted to be used for bioremediation of metal-contaminated and high-salt environments. • Algoriphagus sp. CM16 is a novel Cr(VI)-reducing bacterium from the deep sea. • CM16 can efficiently reduce Cr(VI) under high salt and low temperature conditions. • CM16 has efficient antioxidant enzymes compared to other Cr(VI)-reducing bacteria.