Project description:Methanotrophs, which help regulate atmospheric levels of methane, are active in diverse natural and man-made environments. This range of habitats and the feast-famine cycles seen by many environmental methanotrophs suggest that methanotrophs dynamically mediate rates of methane oxidation. Global methane budgets require ways to account for this variability in time and space. Functional gene biomarker transcripts are increasingly being studied to inform the dynamics of diverse biogeochemical cycles. Previously, per-cell transcript levels of the methane oxidation biomarker, pmoA, were found to vary quantitatively with respect to methane oxidation rates in model aerobic methanotroph, Methylosinus trichosporium OB3b. In the present study, these trends were explored for two additional aerobic methanotroph pure cultures, Methylocystis parvus OBBP and Methylomicrobium album BG8. At steady-state conditions, per cell pmoA mRNA transcript levels strongly correlated with per cell methane oxidation across the three methanotrophs across many orders of magnitude of activity (R2 = 0.91). Additionally, genome-wide expression data (RNA-seq) were used to explore transcriptomic responses of steady state M. album BG8 cultures to short-term CH4 and O2 limitation. These limitations induced regulation of genes involved in central carbon metabolism (including carbon storage), cell motility, and stress response.
Project description:Natural and anthropogenic wetlands are main sources of the atmospheric greenhouse gas methane. Methane emissions from wetlands are mitigated by methanotrophic microorganisms and by processes at the oxic-anoxic interface, such as sulfur cycling, that reduce the activity of methanogens. In this study, we obtained a pure culture (strain HY1) of a versatile wetland methanotroph that oxidizes various organic and inorganic compounds. This strain represents (i) the first isolate that can aerobically oxidize both methane and reduced sulfur compounds and (ii) a new alphapoteobacterial species, named Candidatus Methylovirgula thiovorans. Genomic and proteomic analyses showed that soluble methane monooxygenase and XoxF-type alcohol dehydrogenases are the only enzymes for methane and methanol oxidation, respectively. Unexpectedly, strain HY1 harbors various pathways for respiratory sulfur oxidation and oxidized reduced sulfur compounds to sulfate using the Sox-rDsr pathway (without SoxCD) and the S4I system. It employed the Calvin-Benson-Bassham cycle for CO2 fixation during chemolithoautotrophic growth on the reduced sulfur compounds. Methane and thiosulfate were independently and simultaneously oxidized by strain HY1 for growth. Proteomic and microrespiratory analyses showed that the metabolic pathways for methane and thiosulfate oxidation were induced in the presence of their substrates. The discovery of this versatile methanotroph demonstrates that methanotrophy and thiotrophy is compatible in a single bacterium and adds a new aspect to interactions of methane and sulfur cycles in oxic-anoxic interface environments.
Project description:Nitric oxide (NO) has several important functions in biology and atmospheric chemistry as a toxin, signaling molecule, ozone depleting agent and the precursor of the greenhouse gas nitrous oxide (N2O). Even though NO is a potent oxidant, and was available on earth earlier than oxygen, its direct use by microorganisms for growth was not demonstrated before. Using physiological experiments, metatranscriptomics and metaproteomics, here we show that anaerobic ammonium-oxidizing (anammox) bacterium Kuenenia stuttgartiensis grow by coupling ammonium oxidation to NO reduction, and produce only N2. Such a metabolism could have existed on early earth, and has implications in controlling N2O and NO emissions both from natural and manmade ecosystems, where anammox bacteria contribute significantly to N2 release to the atmosphere.
Project description:Our goal is to convert methane efficiently into liquid fuels that may be more readily transported. Since aerobic oxidation of methane is less efficient, we focused on anaerobic processes to capture methane, which are accomplished by anaerobic methanotrophic archaea (ANME) in consortia. However, no pure culture capable of oxidizing and growing on methane anaerobically has been isolated. In this study, Methanosarcina acetivorans, an archaeal methanogen, was metabolically engineered to take up methane, rather than to generate it. To capture methane, we cloned the DNA coding for the enzyme methyl-coenzyme M reductase (Mcr) from an unculturable archaeal organism from a Black Sea mat into M. acetivorans to effectively run methanogenesis in reverse. The engineered strain produces primarily acetate, and our results demonstrate that pure cultures can grow anaerobically on methane.
Project description:Four Fe(II) concentrations (0.03, 0.09, 0.12 & 0.75 mM) were tested to investigate the stimulation and inhibition effects of ferrous iron on anammox bacterial activity. RNAs were extracted from the cultures, and the synthesized cDNAs by reverse transcription were used to carry out GeoChip analysis, by which the functional communities and expression level differences in functional genes under different Fe(II) concentrations conditions were obtained, and the response of anammox bacteria to Fe(II) stimulation and inhibition are speculated.