Global co‐occurrence of methanogenic archaea and methanotrophic bacteria in Microcystis aggregates

Abstract

Summary Global warming and eutrophication contribute to the worldwide increase in cyanobacterial blooms, and the level of cyanobacterial biomass is strongly associated with rises in methane emissions from surface lake waters. Hence, methane‐metabolizing microorganisms may be important for modulating carbon flow in cyanobacterial blooms. Here, we surveyed methanogenic and methanotrophic communities associated with floating Microcystis aggregates in 10 lakes spanning four continents, through sequencing of 16S rRNA and functional marker genes. Methanogenic archaea (mainly Methanoregula and Methanosaeta) were detectable in 5 of the 10 lakes and constituted the majority (~50%–90%) of the archaeal community in these lakes. Three of the 10 lakes contained relatively more abundant methanotrophs than the other seven lakes, with the methanotrophic genera Methyloparacoccus, Crenothrix, and an uncultured species related to Methylobacter dominating and nearly exclusively found in each of those three lakes. These three are among the five lakes in which methanogens were observed. Operational taxonomic unit (OTU) richness and abundance of methanotrophs were strongly positively correlated with those of methanogens, suggesting that their activities may be coupled. These Microcystis‐aggregate‐associated methanotrophs may be responsible for a hitherto overlooked sink for methane in surface freshwaters, and their co‐occurrence with methanogens sheds light on the methane cycle in cyanobacterial aggregates.

Multiple sources of aerobic methane production in aquatic ecosystems include bacterial photosynthesis

“…2b ). Following earlier work 8 , 28 , 16S rRNA and mcrA sequences were affiliated with the Methanosaeta and Methanospirillum genera, indicating the potential for hydrogenotrophic and acetoclastic (but not methylotrophic) methanogenesis 28 . (Incubations were also monitored to confirm that they were under oxic conditions at all times; Table S1 .)…”

Coexistence of Synechococcus and Microcystis Blooms in a Tropical Urban Reservoir and Their Links with Microbiomes

“…In fact, in our study, 88% of the archaeal methanogens (Methanobacteriales, Methanomicrobiales, Methanosarcinales, and Methanomassiliicoccales) did not correlate to the Methylacidiphilaceae. This points to a possible interaction between Synechococcus and Methylacidiphilaceae, as methanogen and methanotroph, demonstrated in the Microcystis phycosphere . Nevertheless, the potential involvement between Methylacidiphilaceae and cyanobacteria in the oxic methane cycle is still a subject of further investigation.…”

“…Reports on Microscillacaea are limited, and their ecological role is unclear. Yet, all the available studies have related this microbe group to Microcystis aggregates, − implying that the heterotrophs possess unique functional potential linked to the proliferation of Microcystis . A study on methane oxidation activity within Microcystis blooms has shown enriched Microscillacaea in lakes when methane-oxidizing bacteria (MOB) increased .…”

Methane-Derived Carbon as a Driver for Cyanobacterial Growth

“…Hence, the Methylocystis-type sequences we obtained from cyanobacterial isolates (Supplementary Table 4) match this idea of oligotrophic strains being able to survive in the cyanosphere. Additionally, other methanotrophs may be able to survive in the cyanosphere under natural conditions, where large amounts of methane may be formed during cyanobacterial blooms (Li et al, 2021). Another option for supporting MOB growth and activity may be hydrogen gas that is generated during nitrogen fixation by cyanobacteria (Lopes Pinto et al, 2002;Dutta et al, 2005).…”

“…We tested this hypothesis under laboratory conditions, first testing the possibility of cyanobacteria growth in the presence of methane and methanotrophic bacteria without external input of CO 2 , and second, testing the 13 C transfer from CH 4 to cyanobacteria. Since we had no access to axenic cultures of cyanobacteria and there are known examples of methanogens and MOB associations with phytoplankton (Grossart et al, 2011;Mulhollem et al, 2016;Samad et al, 2020;Li et al, 2021), we decided to test the possibility of carbon transfer via MOB metabolites utilized by other organisms that later release CO 2 or organic substances. We also tested the influence of light conditions on the overall performance of the consortium.…”