Methanol utilizers of the rhizosphere and phyllosphere of a common grass and forb host species

Abstract Background: Managed grasslands are global sources of atmospheric methanol, which is one of the most abundant volatile organic compounds (VOCs) in the atmosphere and promotes oxidative capacity for tropospheric and stratospheric ozone depletion. The phyllosphere is a favoured habitat of plant-colonizing methanol-utilizing bacteria. These bacteria also occur in the rhizosphere, but their relevance for methanol consumption and ecosystem fluxes is unclear. Methanol utilizers of the plant-associated microbiota are key for the mitigation of methanol emission through consumption. However, information about grassland plant microbiota members, their biodiversity and metabolic traits, and thus key actors in the global methanol budget is largely lacking.Results: We investigated the methanol utilization and consumption potentials of two common plant species ( Festuca arundinacea and Taraxacum officinale ) in a temperate grassland. The selected grassland exhibited net methanol emission. The detection of 13 C derived from 13 C-methanol in 16S rRNA of the plant microbiota by stable isotope probing (SIP) revealed distinct methanol utilizer communities in the phyllosphere, roots and rhizosphere but not between plant host species. The phyllosphere was colonized by members of Gamma - and Betaproteobacteria . In the rhizosphere, 13 C-labelled Bacteria were affiliated with Deltaproteobacteria , Gemmatimonadates, and Verrucomicrobiae. Less-abundant 13 C-labelled Bacteria were affiliated with well-known methylotrophs of Alpha -, Gamma -, and Betaproteobacteria . Additional metagenome analyses of both plants were consistent with the SIP results and revealed Bacteria with methanol dehydrogenases (e.g., MxaF1 and XoxF1-5 ) of known but also unusual genera (i.e., Methylomirabilis , Methylooceanibacter , Gemmatimonas , Verminephrobacter ). 14 C-methanol tracing of alive plant material revealed divergent methanol oxidation rates in both plant species but similarly high rates in the rhizosphere and phyllosphere.Conclusions: Our study revealed the rhizosphere as an overlooked hotspot for methanol consumption in temperate grasslands. We also identified unusual methanol utilizers in the phyllosphere and rhizosphere. We did not observe a plant host-specific methanol utilizer community. Our results suggest a model for methanol turnover in which both the sources (plants) and sinks (microbiota) of a volatile are separated but in the same ecological unit.