Project description:Aerobic methanotrophic bacteria use methane as their sole source of carbon and energy and serve as a major sink for the potent greenhouse gas methane in freshwater ecosystems. Despite this important environmental role, little is known about the molecular details of how these organisms interact in the environment. Many bacterial species use quorum sensing systems to regulate gene expression in a density-dependent manner. We have identified a quorum sensing system in the genome of Methylobacter tundripaludum, a dominant methane-oxidizer in methane enrichments of sediment from Lake Washington (Seattle, WA, USA). We determined that M. tundripaludum primarily produces N-3-hydroxydecanoyl-L-homoserine lactone (3-OH-C10-HSL) and that production is governed by a positive feedback loop. We then further characterized this system by determining which genes are regulated by quorum sensing in this methane-oxidizer using RNA-seq, and discovered this system regulates the expression of a novel nonribosomal peptide synthetase biosynthetic gene cluster. These results identify and characterize a mode of cellular communication in an aerobic methane-oxidizing bacterium.
Project description:Maider J. Echeveste Medrano and colleagues characterized the physiological and metabolic response of freshwater methanotrophic archaea to salt stress. The study performed metaproteomics, gene expression profiles and dedicated metabolomics to identify the pathways involved in the salt stress response and the osmolyte present in anaerobic methanotrophic archaea. Correspondence to Cornelia U. Welte c.welte@science.ru.nl
Project description:Aerobic methanotrophic bacteria use methane as their sole source of carbon and energy and serve as a major sink for the potent greenhouse gas methane in freshwater ecosystems. Despite this important environmental role, little is known about the molecular details of how these organisms interact in the environment. Many bacterial species use quorum sensing systems to regulate gene expression in a density-dependent manner. We have identified a quorum sensing system in the genome of Methylobacter tundripaludum, a dominant methane-oxidizer in methane enrichments of sediment from Lake Washington (Seattle, WA, USA). We determined that M. tundripaludum primarily produces N-3-hydroxydecanoyl-L-homoserine lactone (3-OH-CÂ10-HSL) and that production is governed by a positive feedback loop. We then further characterized this system by determining which genes are regulated by quorum sensing in this methane-oxidizer using RNA-seq, and discovered this system regulates the expression of a novel nonribosomal peptide synthetase biosynthetic gene cluster. These results identify and characterize a mode of cellular communication in an aerobic methane-oxidizing bacterium. Samples are 2 sets of biological replicates of a Methylobacter tundripaludum strain 21/22 mutant where the acyl-homoserine lactone (AHL) synthase gene mbaI (T451DRAFT_0796) has been deleted. The mutant strain was grown to log (48 hours) or stationary (68 hours) phase in the absence or presence of the AHL 3-OH-C10-HSL.
Project description:Methane is a very potent greenhouse gas and can be oxidized aerobically or anaerobically through microbe-mediated processes, thus decreasing methane emissions in the atmosphere. Using a complementary array of methods, including phylogenetic analysis, physiological experiments, and light and electron microscopy techniques (including electron tomography), we investigated the community composition and ultrastructure of a continuous bioreactor enrichment culture, in which anaerobic oxidation of methane (AOM) was coupled to nitrate reduction. A membrane bioreactor was seeded with AOM biomass and continuously fed with excess methane. After 150 days, the bioreactor reached a daily consumption of 10 mmol nitrate · liter-1 · day-1 The biomass consisted of aggregates that were dominated by nitrate-dependent anaerobic methane-oxidizing "Candidatus Methanoperedens"-like archaea (40%) and nitrite-dependent anaerobic methane-oxidizing "Candidatus Methylomirabilis"-like bacteria (50%). The "Ca Methanoperedens" spp. were identified by fluorescence in situ hybridization and immunogold localization of the methyl-coenzyme M reductase (Mcr) enzyme, which was located in the cytoplasm. The "Ca Methanoperedens" sp. aggregates consisted of slightly irregular coccoid cells (∼1.5-μm diameter) which produced extruding tubular structures and putative cell-to-cell contacts among each other. "Ca Methylomirabilis" sp. bacteria exhibited the polygonal cell shape typical of this genus. In AOM archaea and bacteria, cytochrome c proteins were localized in the cytoplasm and periplasm, respectively, by cytochrome staining. Our results indicate that AOM bacteria and archaea might work closely together in the process of anaerobic methane oxidation, as the bacteria depend on the archaea for nitrite. Future studies will be aimed at elucidating the function of the cell-to-cell interactions in nitrate-dependent AOM.IMPORTANCE Microorganisms performing nitrate- and nitrite-dependent anaerobic methane oxidation are important in both natural and man-made ecosystems, such as wastewater treatment plants. In both systems, complex microbial interactions take place that are largely unknown. Revealing these microbial interactions would enable us to understand how the oxidation of the important greenhouse gas methane occurs in nature and pave the way for the application of these microbes in wastewater treatment plants. Here, we elucidated the microbial composition, ultrastructure, and physiology of a nitrate-dependent AOM community of archaea and bacteria and describe the cell plan of "Ca Methanoperedens"-like methanotrophic archaea.