Project description:Candidatus Pelagibacter ubique is the most abundant marine microorganism, but is unable to utilize inorganic sulfur compounds that are plentiful in the ocean. To investigate how these cells adapt to organic sulfur limitation, batch cultures were grown in defined media containing either limiting or non-limiting amounts of dimethylsulfoniopropionate (DMSP) as the sole sulfur source. Protein and mRNA expression were measured during exponential growth, immediately prior to stationary phase, and in late stationary phase. Two distinct responses were observed: one as DMSP approached exhaustion, and another after the DMSP supply was depleted. The first response was characterized by increased transcription and translation of all Ca. P. ubique genes downstream of previously confirmed S-adenosyl methionine (SAM) riboswitches: bhmT, mmuM, and metY. These genes were up to 33 times more abundant during low DMSP conditions and shunt all available sulfur to methionine. The osmotically inducible organic hydroperoxidase OsmC was the most up-regulated protein as DMSP (an osmolyte) became scarce. The second response, during sulfur-depleted stationary phase, saw increased transcription of the heme c shuttle ccmC and two small genes of unknown function (SAR11_1163 and SAR11_1164) which were 6-10 times higher in sulfur-starved cultures. No known membrane transporters were up-regulated in response to sulfur limitation, suggesting that this bacterium's strategy for coping with sulfur stress focuses on intracellularly redistributing, rather than importing, organic sulfur compounds. This supports the conclusion that the few organosulfur molecules that Ca. P. ubique is able to metabolize are rarely limiting in the marine environment.
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:Candidatus Pelagibacter ubique is the most abundant marine microorganism, but is unable to utilize inorganic sulfur compounds that are plentiful in the ocean. To investigate how these cells adapt to organic sulfur limitation, batch cultures were grown in defined media containing either limiting or non-limiting amounts of dimethylsulfoniopropionate (DMSP) as the sole sulfur source. Protein and mRNA expression were measured during exponential growth, immediately prior to stationary phase, and in late stationary phase. Two distinct responses were observed: one as DMSP approached exhaustion, and another after the DMSP supply was depleted. The first response was characterized by increased transcription and translation of all Ca. P. ubique genes downstream of previously confirmed S-adenosyl methionine (SAM) riboswitches: bhmT, mmuM, and metY. These genes were up to 33 times more abundant during low DMSP conditions and shunt all available sulfur to methionine. The osmotically inducible organic hydroperoxidase OsmC was the most up-regulated protein as DMSP (an osmolyte) became scarce. The second response, during sulfur-depleted stationary phase, saw increased transcription of the heme c shuttle ccmC and two small genes of unknown function (SAR11_1163 and SAR11_1164) which were 6-10 times higher in sulfur-starved cultures. No known membrane transporters were up-regulated in response to sulfur limitation, suggesting that this bacterium's strategy for coping with sulfur stress focuses on intracellularly redistributing, rather than importing, organic sulfur compounds. This supports the conclusion that the few organosulfur molecules that Ca. P. ubique is able to metabolize are rarely limiting in the marine environment. Batch cultures of P. ubique were grown in a defined arificial seawater media. Five cultures were amended with a limiting concentration of DMSP as the sole sulfur source and another four control cultures were amended with a non-limiting DMSP concentration. Cultures were harvested for microarray analyses at multiple timepoints for the purpose of observing differences in gene expression related to sulfur limitation. Proteomic analyses were conducted in parallel and are available at https://www.ebi.ac.uk/pride/archive/projects/PXD003672 .
Project description:P. ubique was investigated to understand the response to limited sulfur in seawater. Sulfur absorption was found to be localized to a rapidly evolving region of the genome.