[Objective]Cr(Ⅲ)often occurs together with Mn-oxidizing bacteria in natural environments.Manga-nese oxides,which are commonly generated from the biotic oxidation of Mn2+by Mn(Ⅱ)-oxidizing bacteria,and are considered the main oxidants of Cr(Ⅲ)in nature.[Methods]Investigating the impact of Cr(Ⅲ)on the ac-tivity and function of Mn(Ⅱ)-oxidizing bacteria is important for understanding Mn cycling and the transformation of Cr in natural environments.In this study,Pseudomonas putida MnB1 was chosen as a representative Mn(Ⅱ)-oxi-dizing bacterium,and the effect and mechanisms of Cr(Ⅲ)on the activity and function of MnB1 were investigated by batch experiments.[Results]The results showed that Cr(Ⅲ)at a concentration higher than 0.05 mmol/L Cr(Ⅲ)caused significant death of MnB1,and the bactericidal effect became stronger with increasing Cr(Ⅲ)con-centration.The concentration of Cr(Ⅲ)higher than 0.02 mmol/L Cr(Ⅲ)delayed the biotic oxidation of Mn(Ⅱ),and 0.2 mmol/L Cr(Ⅲ)completely inhibited the oxidation of Mn(Ⅱ).A mechanistic study revealed that the intracellular reactive oxygen species(ROS)induced by Cr(Ⅲ)and cell membrane permeability changes caused by Cr(Ⅲ)particles collaboratively inhibited the metabolism and function of MnB1.[Conclusion]This study provides a new theoretical basis for further understanding the biogeochemical cycle of manganese and the mi-gration and transformation behavior of chromium in the natural environment.
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