Distribution et abondance de microorganismes méthagéniques et méthatrophes dans les cours d'eau européens

International audienceGlobally, streams and rivers emit a significant amount of methane, a highly potent greenhouse gas. However, little is known about stream sediment microbial communities, driving the net methane balance in these systems, especially on their distribution and composition at large spatial scales. Within the project Euro Methane we investigated the diversity and abundance of methanogenic archaea and methane-oxidizing bacteria across 16 European streams (from northern Spain to central Sweden) via 16S rRNA sequencing and qPCR. We determined environmental drivers of both abundance and community composition and explored the link to measured potential methane production and oxidation rates of the respective sediments. We found that the community composition of methane-oxidizing bacteria significantly differed among the studied streams, while methanogenic archaea were more homogeneously distributed. Beyond the overall diversity trends, indicator species for stream types were identified. Methanogenic Methanosaeta sp. and methane-oxidizing Methyloglobulus sp. increased with geographical latitude and dominated in headwater streams (orders 1-3) with high oxygen levels and high proportions of pristine land within the catchment, while methanogenic Methanomethylovorans sp. and methane-oxidizing Methylocaldum spp. were more common in larger streams (orders 4-6) with higher discharge and agricultural influence. Potential methane production rates significantly increased with abundance of methanogenic archaea, while potential methane oxidation rates did not show significant correlations with methane oxidizing bacteria, presumably due to the more diverse physiological capabilities of this microbial group. Our study represents a holistic large-scale biogeographical overview of two microbial groups to enhance our understanding of the methane cycle within a heretofore understudied ecosystem

Abundance and biogeography of methanogenic and methanotrophic microorganisms across European streams

Aim Although running waters are getting recognized as important methane sources, large-scale geographical patterns of microorganisms controlling the net methane balance of streams are still unknown. Here we aim at describing community compositions of methanogenic and methanotrophic microorganisms at large spatial scales and at linking their abundances to potential sediment methane production (PMP) and oxidation rates (PMO). Location The study spans across 16 European streams from northern Spain to northern Sweden and from western Ireland to western Bulgaria. Taxon Methanogenic archaea and methane-oxidizing microorganisms. Methods To provide a geographical overview of both groups in a single approach, microbial communities and abundances were investigated via 16S rRNA gene sequencing, extracting relevant OTUs based on literature; both groups were quantified via quantitative PCR targeting mcrA and pmoA genes and studied in relation to environmental parameters, sediment PMP and PMO, and land-use. Results Diversity of methanogenic archaea was higher in warmer streams and of methanotrophic communities in southern sampling sites and in larger streams. Anthropogenically-altered, warm and oxygen-poor streams were dominated by the highly efficient methanogenic families Methanospirillaceae, Methanosarcinaceae, and Methanobacteriaceae, but did not harbor any specific methanotrophic organisms. Contrastingly, sediment communities in colder, oxygen-rich waters with little anthropogenic impact were characterised by methanogenic Methanosaetaceae, Methanocellaceae and Methanoflorentaceae and methanotrophic Methylococcaceae and Cd. Methanoperedens. Representatives of the methanotrophic Crenotrichaceae and Methylococcaceae as well as the methanogenic Methanoregulaceae were characteristic for environments with larger catchment area and higher discharge. PMP increased with increasing abundance of methanogenic archaea, while PMO rates did not show correlations with abundances of methane oxidizing bacteria. Main conclusions Methanogenic and methanotrophic communities grouping into three habitat types suggest that future climate- and land-use changes may influence the prevailing microbes involved in the large-scale stream-related methane cycle, favoring the growth of highly efficient hydrogenotrophic methane-producers. Based on these results, we expect global change effect on PMP rates to especially impact rivers adjacent to anthropogenically disturbed land-uses

Impacts of diffuse urban stressors on stream benthic communities and ecosystem functioning: A review

Catchment urbanisation results in urban streams being exposed to a multitude of stressors. Notably, stressors originating from diffuse sources have received less attention than stressors originating from point sources. Here, advances related to diffuse urban stressors and their consequences for stream benthic communities are summarised by reviewing 92 articles. Based on the search criteria, the number of articles dealing with diffuse urban stressors in streams has been increasing, and most of them focused on North America, Europe, and China. Land use was the most common measure used to characterize diffuse stressor sources in urban streams (70.7 % of the articles characterised land use), and chemical stressors (inorganic nutrients, xenobiotics, metals, and water properties, including pH and conductivity) were more frequently reported than physical or biological stressors. A total of 53.3 % of the articles addressed the impact of urban stressors on macroinvertebrates, while 35.9 % focused on bacteria, 9.8 % on fungi, and 8.7 % on algae. Regarding ecosystem functions, almost half of the articles (43.5 %) addressed changes in community dynamics, 40.3 % addressed organic matter decomposition, and 33.9 % addressed nutrient cycling. When comparing urban and non-urban streams, the reviewed studies suggest that urbanisation negatively impacts the diversity of benthic organisms, leading to shifts in community composition. These changes imply functional degradation of streams. The results of the present review summarise the knowledge gained to date and identify its main gaps to help improve our understanding of urban streams.This study has received funding from the Iberian Association of Limnology (AIL) through the project URBIFUN (Urbanization effects on the relationship between microbial biodiversity and ecosystem functioning), awarded to Míriam Colls and Ferran Romero. Authors thank as well the Basque Government (Consolidated Research Group IT951-16) and the MERLIN project 101036337 – H2020-LC-GD-2020/H2020-LC-GD-2020-3.info:eu-repo/semantics/publishedVersio