Physiological Significance of Bacterial Mn(II) Oxidation

Abstract Bacterial oxidation of Mn(II) to Mn(III/IV) oxides is widespread in nature and proceeds markedly faster than abiotic oxidation. However, the physiological role of this process remains unclear. Building on recent evidence that environmental stress determines bacterial Mn(II)-oxidation activity, we used Pseudomonas putida KT2440—a known Mn(II)-oxidizing bacterium—to investigate the potential drivers and benefits of this reaction. Using RNA-seq, we observed up-regulation of starvation-related two-component system genes during Mn(II) oxidation, supporting the idea that nutrient limitation acts as a trigger. This led us to hypothesize that introducing an external antagonistic stressor could further accelerate the onset and rate of Mn(II) oxidation. To test this, we established a synthetic microbial community in which KT2440 was confronted with Pseudomonas aeruginosa PAO1, which possesses both contact-dependent and diffusible antagonistic systems. Across multiple assays measuring oxidation initiation time, manganese oxide accumulation, and bacterial survival, the presence of PAO1 significantly accelerated Mn(II) oxidation by KT2440. More importantly, Mn(II) oxidation strongly enhanced KT2440 survival under antagonistic pressure. Correlation analysis indicated a positive relationship between survival rate and oxidation intensity. Fluorescence microscopy and agent-based modeling further confirmed that this protective effect is contact-dependent. By integrating these results with earlier findings, we propose that the physiological significance of bacterial Mn(II) oxidation lies in enhancing the survival fitness of the oxidizer under stressful conditions.