Project description:Dinoflagellate blooms are natural phenomena that have drawn global attention due to their huge negative impacts on marine ecosystems, mariculture and human health. Although the understanding of dinoflagellate blooms has been significantly improved over the past half century, little is known about the underlying mechanisms sustaining the high biomass growth rate during the bloom period which is paradoxically characterized by low dissolved CO2 and inorganic nutrients. Here, we compared the metaproteomes of non-bloom, mid-bloom and late-bloom cells of a marine dinoflagellate Prorocentrum donghaiense in the coastal East China Sea, to understand the underlying mechanisms sustaining high biomass growth rate under the typically low CO2 and inorganic nutrient conditions.
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.
Project description:Harmful algal blooms are induced largely by nutrient enrichment common in warm waters. An increasingly frequent phenomenon is the “red tide”: blooms of dinoflagellate microalgae that accumulate toxins lethal to other organisms in high doses. Here, we present the de novo assembled genome (~4.75 Gbp) of Prorocentrum cordatum, a globally abundant, bloom-forming dinoflagellate, and the associated transcriptome, proteome, and metabolome data from axenic cultures to elucidate the microalgal molecular responses to heat stress. We discovered, in a high-G+C genome with long introns and extensive genetic duplication, a complementary mechanism between RNA editing and exon usage that regulates dynamic expression and functional diversity of genes and proteins, and metabolic profiles that reflect reduced capacities in photosynthesis, central metabolism, and protein synthesis. These results based on multi-omics evidence demonstrate the genomic hallmark of a bloom-forming dinoflagellate, and how the complex gene structures combined with multi-level transcriptional regulation underpin concerted heat-stress responses.
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.
Project description:One of the most abundant organic carbon sources in the ocean is glycolate, a compound that is commonly secreted by marine phytoplankton resulting in an estimated annual flux of one petagram of glycolate in marine environments. While it is generally accepted that glycolate is oxidized to glyoxylate by marine bacteria, the further fate of this C2 metabolite is not well understood. Here we show that ubiquitous marine Proteobacteria are able to assimilate glyoxylate via the hydroxyaspartate cycle (BHAC) that was originally proposed 56 years ago. We unravel the biochemistry of the BHAC and describe the structure of its key enzymes, including a previously unknown primary imine reductase. Overall, the BHAC allows for the direct production of oxaloacetate from glyoxylate through only four enzymatic steps, representing the most efficient glyoxylate assimilation route described to date. Analysis of marine metagenomes shows that the BHAC is globally distributed and on average 20-fold more abundant than the glycerate pathway, the only other known pathway for net glyoxylate assimilation. In a field study on a phytoplankton bloom, we show that glycolate is present in high nanomolar concentrations and taken up by prokaryotes at rates that allow a full turnover of the glycolate pool within one week. During the bloom, the BHAC is present in up to 1.5% of the bacterial community and actively transcribed, supporting its role in glycolate assimilation and suggesting a new trophic interaction between autotrophic phytoplankton and heterotrophic bacterioplankton.
Project description:The objective was to identify functional genes encoded by Fungi and fungal-like organisms to assess putative ecological roles Using the GeoChip microarray, we detected fungal genes involved in the complete assimilation of nitrate and the degradation of lignin, as well as evidence for Partitiviridae (a mycovirus) that likely regulates fungal populations in the marine environment. These results demonstrate the potential for fungi to degrade terrigenously-sourced molecules, such as permafrost and compete with algae for nitrate during blooms. Ultimately, these data suggest that marine fungi could be as important in oceanic ecosystems as they are in freshwater environments.