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Description
Terrestrial ecosystems are often characterized as a main biological sink for methane emissions. While dryland ecosystems represent up to one third of terrestrial ecosystems, very few studies have been carried out on the microbial communities that drive the methane cycle in these ecosystems. Initial studies by our SDSU team within the Anza Borrego Desert State Park revealed that plots of soil with vegetation have higher methane consumption rates compared to plots of soil without vegetation. This led to the hypothesis that there is an association between the desert plants and methane-consuming bacteria (methanotrophs). Here I proposed, that the desert flora contribute to the transport of atmospheric oxygen and methane into the rhizosphere, thus providing a suitable niche for methanotrophs. In this study I carried out an analysis of metagenomic datasets generated in collaboration with the Joint Genomic Institute. The metadata revealed that Methylocaldum and Methylobacter are the dominant methanotrophs in the Anza Borrego Desert soils. Three pure culture of methane consuming bacteria and eleven associated non-methanotrophic bacteria (e.g. satellites) were obtained and their genome sequences were reconstructed. Pure cultures of the most dominant desert methanotroph, Methylocaldum sp. 0917 and its satellite Bradyrhizobium sp. W were used to set up synthetic soil communities with Boechera depauperata, a native California plant species and a model system for investigating plant thermal stress responses. Metabolomic analyses were carried out in order to identify the compounds being exchanged between microbes, and between the microbes and plants in the system. The metabolomic profiling of the microcosm experiments revealed that methane-consuming communities can produce compounds which promote drought resilience in plants, e.g. choline phosphate, nicotinamide riboside, salicylate and trehalose. Additionally, new evidence suggests that Bradyrhizobium sp. W produces vitamin B6, which could benefit the growth of Methylocaldum sp. 0917. Overall, the outcomes of this study revealed Methylocaldum spp. as the main clade of methanotrophic bacteria inhabiting dryland environments. Furthermore, the data suggests that the methane consuming bacterium can promote plant resilience to drought by synthetizing essential nutrients from methane.
