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Comparative proteomics of Alteromonas macleodii cultured with sulfoquinovosyl glycerol

ABSTRACT: Sulfoquinovose (SQ) and sulfoquinovosyl glycerol (SQGro), derived from abundant membrane sulfolipids termed sulfoquinovosyl diacylglycerols (SQDG) produced by photosynthetic organisms, serve as sources of carbon and sulfur for bacteria. The conversion processes of these sulfoquinovosyl compounds (SQ, SQGro, and SQDG) within marine ecosystems, and their quantitative contributions to the marine organic matter pool, are poorly understood. We have identified Alteromonas macleodii, a cosmopolitan marine bacterium, as a novel organism capable of metabolizing SQ and SQGro. A. macleodii possesses a sulfoquinovosidase that converts SQGro to SQ, and is a member of a distinct clade within glycoside hydrolase family 31 distinct from other sulfoqinovosidases. The ubiquitous presence of sulfoquinovosidases and their transcripts throughout marine environments suggests active metabolism of sulfoquinovose glycosides, particularly in the sunlit surface ocean. Complementing these observations, we demonstrate that marine algae and cyanobacteria produce significant quantities of SQGro, and field samples from coastal and open ocean environments enabled estimation of the annual turnover of SQGro in the teragram range. Together with SQDG and SQ, these sulfoquinovosyl compounds constitute a substantial portion of the marine organic sulfur, estimated at around 1.5 petagrams of carbon turnover per annum. These findings reveal a vast, previously unappreciated pool of organosulfonates within the microbial food web that contributes significantly to the marine carbon and sulfur cycles.

INSTRUMENT(S):

ORGANISM(S): Alteromonas Macleodii Atcc 27126

TISSUE(S): Cell Culture

SUBMITTER: Huanyu Wang

LAB HEAD: Kai Tang

PROVIDER: PXD058710 | Pride | 2025-08-25

REPOSITORIES: Pride

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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:The fraction of dissolved dimethylsulfoniopropionate (DMSPd) converted by marine bacterioplankton into the climate-active gas dimethylsulfide (DMS) varies widely in the ocean, with the factors that determine this value still largely unknown. One current hypothesis is that the ratio of DMS formation:DMSP demethylation is determined by DMSP availability, with 'availability' in both an absolute sense (i.e., concentration in seawater) and in a relative sense (i.e., proportionally to other labile organic S compounds) being proposed as the critical factor. We investigated these models during an experimentally-induced phytoplankton bloom using an environmental microarray targeting DMSP-related gene expression in the Roseobacter group, a taxon of marine bacteria known to play an important role in the surface ocean sulfur cycle. The array consisted of 1,578 probes to 431 genes, including those previously linked to DMSP degradation as well as core genes common in sequenced Roseobacter genomes. The prevailing pattern of Roseobacter gene expression showed depletion of DMSP-related transcripts during the peak of the bloom, despite the fact that absolute concentrations and flux of DMSP-related compounds were increasing. A likely interpretation is that DMSPd was assimilated by Roseobacter populations in proportion to its relative abundance in the organic matter pool (the “relative sense” hypothesis), and that it is not taken up in preference to other sources of labile organic sulfur or carbon produced during the bloom. The relative investment of the Roseobacter community in DMSP demethylation did not predict the fractional conversion of DMSP to DMS, however, suggesting a complex regulatory process that may involve multiple fates of DMSPd. DMSP-related gene expression in the Roseobacter group was investigated using an environmental microarray. Coastal seawater from the Gulf of Mexico was collected and dispensed into 20-L microcosms. Two replicate cubitainers were amended with nutrients (N and P) to stimulate phytoplankton bloom, while two untreated cubitainers served as controls. The microcosms were incubated at 27ºC in a temperature-controlled incubator on a 12 h light/dark cycle for total of 7 days. Ten RNA samples (Day 0: 2 conditions with 1 biological replicate each; Days 2 and 4: 2 conditions with 2 biological replicates each) were prepared for microarray hybridization. After total RNA extraction, rRNAs were removed and mRNA transcripts were amplified and labeled with Alexa Fluor 647. Two technical replicates were hybridized from each RNA sample. The microarray was designed based on selected Ruegeria pomeroyi DSS-3 genes and their orthologs in 12 other sequenced Roseobacter genomes. Probes were designed from the orthologs using the Hierarchical Probe Design (HPD) algorithm.

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Comparative proteomics of Alteromonas macleodii cultured with sulfoquinovosyl glycerol

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