Enhanced biogenic manganese oxide production and the removal of Cd(II) and ciprofloxacin via fungus-bacterium co-cultivation

Microbial co-cultivation is a promising strategy for enhancing metabolite production and functional capabilities. While most research on biogenic manganese (Mn) oxidation (BMO) has focused on individual bacterial or fungal strains, the potential benefits of fungal-bacterial co-cultivation remain largely unexplored. In this study, the synergistic effects of co-culturing the Mn-oxidizing fungus Cladosporium sp. XM01 with the Mn-oxidizing bacterium Bacillus sp. XM02 on Mn(II) oxidation were systematically investigated. The results showed that co-cultivation significantly increased total cell biomass and enhanced Mn(II) removal. Optimal conditions were achieved by introducing strain XM02 with a 36 h delay and maintaining a co-culturing ratio of 2:1 (XM01:XM02). The enhanced Mn(II) oxidation observed in the co-culture system was attributed to increased activities of superoxide dismutase and catalase, which help maintain redox homeostasis and sustain the production of superoxide—an essential oxidant in Mn(II) bio-oxidation. Scanning electron microscopy revealed that Bacillus sp. XM02 cells were attached to the hyphae of Cladosporium sp. XM01, forming structured fungal-bacterial aggregates. These aggregates suggest strong physical interactions that likely facilitated nutrient exchange and metabolic cooperation. Additionally, removal kinetics experiments showed that BMO produced in the co-culture exhibited superior Cd(II) adsorption capacity and ciprofloxacin oxidation performance compared to BMO derived from pure cultures. This enhancement was linked to the higher specific surface area and increased average oxidation state (Mn-AOS) of the co-culture BMO, which enhanced its adsorption and oxidative reactivity. These findings provide new insights into the symbiotic interactions among Mn-oxidizing microorganisms and highlight the potential of fungal-bacterial co-cultures as an effective strategy to enhance BMO functionality for environmental remediation.