Nutrient Condition-InducedMechanism Shift of MicrobialManganese Oxidation: Significance of Catalase

Manganese-oxidizing bacteria facilitate manganese oxide formation through direct and indirect oxidation pathways. While nutrient conditions are known to significantly influence microbial metabolism, their impact on microbial manganese oxidation remains unclear. In this study, we explored the microbial manganese oxidation process under varying nutrient conditions. Under eutrophic and mesotrophic conditions, Mn(II) oxidation primarily occurred during the stationary phase, whereas no manganese oxides were detected under oligotrophic conditions. Extracellular superoxide radicals (O₂^•–) were identified as the primary drivers of the manganese oxidation process under oligotrophic conditions. However, O₂^•– reacted with Mn(II) to form hydrogen peroxide (H₂O₂) and Mn(III), with subsequent consumption of H₂O₂ in the reaction with Mn(III), regenerating Mn(II). The addition of catalase (CAT) significantly enhanced Mn(III) production under oligotrophic conditions, reaching a maximum UV₂₅₈ value of 0.24 at 16 h, suggesting that CAT could promote Mn(III) accumulation by consuming H₂O₂, thus increasing the rate of manganese oxide formation. In contrast, under nutrient-rich conditions, manganese oxidation was primarily mediated by multicopper oxidases, where Mn(III) was further oxidized to manganese oxides. Our work highlights the critical role of nutrient conditions in microbial manganese oxidation, which can significantly affect the transformation of manganese in the environment and the effectiveness of water treatment processes.