Microbial Ecology of Methanotrophy in Streams Along a Gradient of CH(4) Availability

Despite the recognition of streams and rivers as sources of methane (CH(4)) to the atmosphere, the role of CH(4) oxidation (MOX) in these ecosystems remains poorly understood to date. Here, we measured the kinetics of MOX in stream sediments of 14 sites to resolve the ecophysiology of CH(4) oxidizing bacteria (MOB) communities. The streams cover a gradient of land cover and associated physicochemical parameter and differed in stream- and porewater CH(4) concentrations. Michealis–Menten kinetic parameter of MOX, maximum reaction velocity (V(max)), and CH(4) concentration at half V(max) (K(S)) increased with CH(4) supply. K(S) values in the micromolar range matched the CH(4) concentrations measured in shallow stream sediments and indicate that MOX is mostly driven by low-affinity MOB. 16S rRNA gene sequencing identified MOB classified as Methylococcaceae and particularly Crenothrix. Their relative abundance correlated with pmoA gene counts and MOX rates, underscoring their pivotal role as CH(4) oxidizers in stream sediments. Building on the concept of enterotypes, we identify two distinct groups of co-occurring MOB. While there was no taxonomic difference among the members of each cluster, one cluster contained abundant and common MOB, whereas the other cluster contained rare operational taxonomic units (OTUs) specific to a subset of streams. These integrated analyses of changes in MOB community structure, gene abundance, and the corresponding ecosystem process contribute to a better understanding of the distal controls on MOX in streams.