Adaptation of methane oxidising bacteria to environmental changes: implications for coastal methane dynamics

Abstract. Global warming induced alterations in ocean temperature regimes, and precipitation patterns are increasingly impacting coastal ecosystems, leading to shifts in water column properties. These changes may have profound implications for microbial communities such as methane-oxidising bacteria (MOBs), which play a critical role in regulating methane fluxes and ecosystem dynamics. In this study, we investigate the resilience and adaptability of aerobic MOBs in response to changing environmental conditions. Through microcosm incubation experiments with waters from the North Sea and the Wadden Sea collected during different seasons, we explore how variations in methane availability, temperature, and salinity influence the MOB community structure and functional capacity. Our results reveal an increase in the relative abundance of MOBs to up to 57 % in experiments with elevated methane concentrations, highlighting the primary role of methane availability for MOB community development. Temperature and salinity variations, on the other hand, exerted lesser effects on MOB composition and relative abundance. A strong effect on MOB community development was furthermore caused by the origin of the inoculum (location and season). Our results thus suggest a functional redundancy in the variable pools of microbial inocula enabling multiple MOB clades to cope with drastic changes in environmental parameters. The adaptability of MOB communities is key to understand their role in mitigating methane emissions from coastal regions in a future ocean with potentially elevated methane, temperature and variable salinity levels.