Methanotrophic potential of Dutch canal wall biofilms is driven by Methylomonadaceae

Global urbanization of waterways over the past millennium has influenced microbial communities in these aquatic ecosystems. Increased nutrient inputs have turned most urban waters into net sources of the greenhouse gases carbon dioxide (CO(2)) and methane (CH(4)). Here, canal walls of five Dutch cities were studied for their biofilm CH(4) oxidation potential, alongside field observations of water chemistry, and CO(2) and CH(4) emissions. Three cities showed canal wall biofilms with relatively high biological CH(4) oxidation potential up to 0.48 mmol g(DW)(−1) d(−1), whereas the other two cities showed no oxidation potential. Salinity was identified as the main driver of biofilm bacterial community composition. Crenothrix and Methyloglobulus methanotrophs were observed in CH(4)-oxidizing biofilms. We show that microbial oxidation in canal biofilms is widespread and is likely driven by the same taxa found across cities with distinctly different canal water chemistry. The oxidation potential of the biofilms was not correlated with the amount of CH(4) emitted but was related to the presence or absence of methanotrophs in the biofilms. This was controlled by whether there was enough CH(4) present to sustain a methanotrophic community. These results demonstrate that canal wall biofilms can directly contribute to the mitigation of greenhouse gases from urban canals.