Beyond Manganese Oxidizing Bacteria: Using Metagenomics for an Improved Understanding of Sustained Manganese Oxidation and Removal in Surface Water Biofilters

Abstract

Manganese has evolved from a contaminant of aesthetic concern due to an improved understanding of the health risks associated with elevated levels of Mn in drinking water and its accumulation within, and subsequent release from, distribution systems. Utilities require sustainable treatment options to minimize Mn concentrations in finished water, such as biofiltration. While this is an established and effective treatment for Mn in groundwater, there is limited research on biological Mn removal in surface water treatment plants. To address this knowledge gap multiple studies were conducted to understand (1) the impact of source water type on biofilter microbiome and biofilm composition, (2) physico-chemical and biological mechanisms of Mn oxidation and removal during the start-up of new biofilters, as well as factors which may accelerate biofilter acclimation, and (3) taxonomic and functional targets within microbial communities that contribute to sustained Mn removal performance despite seasonal fluctuations in influent water temperature. Source water type was observed to influence microbiome composition and resulted in distinctions between biofilters at mixed-water and groundwater treatment plants. Interactions between water chemistry and filter media strongly influenced the rate of acclimation in new Mn removing biofilters, however development of an acclimated microbiome was required for sustained Mn removal in the absence of physico-chemical mechanisms. Co-occurrence relationships between Betaproteobacteria and other taxa within the microbial community were a key component of mature biofilters with sustained Mn removal despite seasonal fluctuations in influent water temperature. Further, the absence of these taxa, and the subsequent disruption of their co-occurrence relationships within the microbial community, may have contributed to observed decreases in Mn removal concurrent with decreases in influent water temperature. Enriched functional genes within Betaproteobacteria were related to intercellular interactions, including production and transport of micro-nutrients between taxa, formation and modification of a shared biofilm, and key pathways for energy metabolism. Within the larger Betaproteobacteria class, taxonomic and functional analysis identified the Comamonadaceae, Sphaerotilaceae, and Nitrosomonadaceae families as potential targets of interest for future studies. These results provide valuable insight into optimizing sustainable Mn biofiltration, thereby aiding surface water utilities in minimizing finished water Mn concentrations and achieving year-round Mn performance.