BayCEER Workshop 2025

Chemolithoautotrophic bacteria at the intersection of multiple element cycles in Mn oxidizing biofilms from a hydropower plant maintenance tunnel

P 10 in Posters

Subsurface groundwater habitats devoid of light and poor in organic carbon and nutrients can host diverse microbial communities with not yet fully understood ecophysiologies.

Here we report on the discovery of viscous fast-growing biofilms that represent a massive enrichment of methane-oxidizing, nitrogen cycling, and manganese oxidizing microorganisms in the maintenance tunnel of a hydropower plant.

Chemical analysis revealed that the seepage water contained strongly elevated concentrations of methane, as well as elevated ammonium and manganese concentrations. After passing through the biofilm, methane, ammonium and dissolved manganese were removed from the water. Batch incubation showed that live biofilm oxidizes manganese 80% faster than the abiotic auto-oxidation process.

Based on 16S rRNA gene sequencing, black biofilms were dominated by various methano- and methylotrophic Gammaproteobacteria with Methylococcales making up to 25% highlighting methane as the system’s primary energy source. However, the biofilms also contained nitrogen-cycling organisms like Nitrospira and other uncultured freshwater taxa with uncertain metabolic function. Orange biofilms, poor in Mn oxides, contained large coccoid cells with strong orange and blue auto-fluorescence. They were dominated by Bacteroidota and Burkholderiales.

Searches of metal-oxidation genes among the closest related available genomes identified Acidobacteriota, Nitrospira and diverse Gammaproteobacteria including Methylococcales as potential manganese oxidizers. Further incubation and enrichment experiments with different combinations of electron donors to disentangle the function and activity of different chemolithoautotrophs are underway.

Collectively, a remarkably active chemolithotrophic microbial ecosystem was discovered, which has great potential to elucidate the ecophysiologies of diverse freshwater chemolithotrophs and the interplay of methane, ammonia, and manganese oxidation.

Keywords: biofilms, chemolithoautotrophy, manganese oxidation, methane oxidation, groundwater, subsurface microbiology, microbial communities