Reactive oxygen species (ROS) are a kind of oxygen-containing chemical substances with higher chemical reactivity than oxygen molecules. During the Mesoproterozoic, Earth's oxygen level increased continually, accompanied by the appearance of a large number of ROS components, which is highly destructive to living organisms. In modern studies, nanosized minerals called nanozymes present enzyme-like activities such as catalase, superoxide dismutase and peroxidase. Therefore we hypothesis that iron-containing and manganese-containing nanoparticles in ancient ocean have ROS scavenge ability that help microorganisms avoid ROS stress. In that case, we synthesized ferrihydrite nanoparticle with different silicon-iron ratio and birnessite nanoparticle to investigate antioxidant enzyme activities. Then the S.oneidensis WP3 strain was selected, cells were added to the mineral suspension with H₂O₂ to simulate ROS stress. The results show that both ferrihydrite and birnessite nanoparticles have catalase-like activities that can decompose H₂O₂ to H₂O and O₂. In H₂O₂ threaten experience, cells of WP3 strain can survive in 100μM of H₂O₂ by adding ferrihydrite and birnessite while they were suffered in the same H₂O₂ concentration without nanozymes addition. Finally we added ferrihydrite and birnessite in the medium for cell culture and investigate the growth condition of WP3 strain. The result showed that WP3 strain with the addition of nanoparticles grow better than control group and have less H₂O₂ and ·OH in the system. The findings of this study gives a new horizon of antioxidant pathway by microorganisms in ancient ocean.

Reactive Oxygen Species; Nanozymes; Ferrihydrite；Birnessite