Project description:Polysaccharides from macroalgae are important bacterial nutrient source and central biogeochemical component in the oceans. To illuminate the cellular mechanisms of polysaccharide degradation by marine bacteria, growth of Alteromonas macleodii 83-1 on a mix of laminarin, alginate and pectin was characterized using transcriptomics, proteomics and exometabolomics. A. macleodii 83-1 showed two distinct growth stages, with exponential growth during laminarin utilization followed by maintenance during simultaneous alginate/pectin utilization. The biphasic growth coincided with major temporal shifts in gene expression and metabolite secretion, enabling to define major/accessory polysaccharide utilization loci, reconstruct the complete degradation pathways for each polysaccharide, as well as identify temporal phenotypes in other relevant traits. FT-ICR-MS revealed a distinct suite of secreted metabolites for each growth phase, with pyrroloquinoline quinone exclusively produced with alginate/pectin. The finding of substrate-unique phenotypes indicates an exquisite adaptation to polysaccharide utilization with probable relevance for the degradation of macroalgal biomass, which comprises a complex mix of polysaccharides. Moreover, substrate-unique exometabolomes possibly influence metabolic interactions with other community members. Overall, the presence of fine-tuned genetic machineries for polysaccharide degradation and the widespread detection of related CAZymes in global locations indicate an ecological relevance of A. macleodii in marine polysaccharide cycling and bacteria-algae interactions.
Project description: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.
Project description: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.
Project description:Phytoplankton-bacteria interactions are pivotal in marine ecosystems, influencing primary production and biogeochemical cycles. Diatoms engage in diverse relationships with bacteria, ranging from mutualism to pathogenicity. This study explores the interaction between a novel Alteromonas macleodii strain from the Equatorial Pacific and the model Thalassiosira pseudonana across the diatom different growth phases. We demonstrate that A. macleodii’s algicidal activity depends on the diatom’s growth phase, defensive capacity, and nutrient availability. The algicidal effect manifests during the diatom’s stationary phase or with external nutrient supplementation, implicating organic matter availability as a key driver. Transcriptomic analysis reveals that A. macleodii shifts from motility-associated to growth-associated gene expression based on the diatom’s physiology and coculture duration. Filtrate assays and fluorescence microscopy suggest a two-stage infection model: initial bacterial motility and exudate secretion induce diatom death, followed by bacterial aggregation around debris. Comparative transcriptomics with other algal hosts highlights host-specific bacterial responses, underscoring the context-dependent nature of these interactions. Our findings provide a deeper understanding of the molecular mechanisms driving diatom-bacteria interactions, shedding light on their role in marine microbial ecology and ecosystem functioning.