Enhancing passive bioremediation systems through isolation and reintroduction of native manganese-oxidizing microorganisms

Manganese (Mn) is an essential micronutrient, but anthropogenic activities can generate Mn-rich waste streams that have the potential to threaten human and ecosystem health. A promising low-cost, efficient, and environmentally-friendly remediation strategy involves using Mn-oxidizing bacteria to precipitate aqueous Mn(II) as insoluble Mn(III/IV) oxides. In this study, we investigated the potential for bioaugmentation of native Mn-oxidizing organisms to remediate a site receiving water with high Mn concentrations (up to 3.7 mM). Microbial community analysis revealed that up to 9.6% of native Mn-oxidizing bacteria belonged to the Pseudomonadota phylum, with Pseudomonas putida as the dominant species. Enrichment with amino acid-rich carbon sources increased the relative abundance of this phylum to 35.6%. However, these communities were unable to oxidize Mn(II) above 1 mM, likely due to inhibition of Mn-oxidizing enzymes at concentrations >200 µM. This limitation was overcome by introducing Mn(II) in increasingly higher doses. This strategy enabled the formation of reactive biogenic Mn oxides through enzymatic and subsequently abiotic reactions, achieving up to 2.4 mM Mn(II) removal within six days under controlled conditions. Overall, this study offers a targeted approach to isolate and identify native Mn oxidizers, which can subsequently be selected for implementation of site-specific bioremediation strategies.