Project description:Marine microalgae (phytoplankton) mediate almost half of the worldwide photosynthetic carbon dioxide fixation and therefore play a pivotal role in global carbon cycling, most prominently during massive phytoplankton blooms. Phytoplankton biomass consists of considerable proportions of polysaccharides, substantial parts of which are rapidly remineralized by heterotrophic bacteria. We analyzed the diversity, activity and functional potential of such polysaccharide-degrading bacteria in different size fractions during a diverse spring phytoplankton bloom at Helgoland Roads (southern North Sea) at high temporal resolution using microscopic, physicochemical, biodiversity, metagenome and metaproteome analyses.
Project description:The spring bloom in the North Atlantic develops over a few weeks in response to the physical stabilization of the nutrient replete water column and is one of the biggest biological signals on earth. The composition of the phytoplankton assemblage during the spring bloom of 2008 was evaluated, using a microarray, on the basis of functional genes that encode key enzymes in nitrogen and carbon assimilation in eukaryotic and prokaryotic phytoplankton. Oligonucleotide archetype probes representing RuBisCO, nitrate reductase and nitrate transporter genes from major phytoplankton classes detected a diverse assemblage. For RuBisCO, the archetypes with strongest signals represented known phytoplankton groups, but for the nitrate related genes, the major signals were not closely related to any known phytoplankton sequences. Most of the assemblage's components exhibited consistent temporal/spatial patterns. Yet, the strongest archetype signals often showed quite different patterns, indicating different ecological responses by the main players. The most abundant phytoplankton genera identified previously by microscopy, however, were not well represented on the microarray. The lack of sequence data for well-studied species, and the inability to identify organisms associated with functional gene sequences in the environment, still limits our understanding of phytoplankton ecology even in this relatively well-studied system.
Project description:The marine diatom Guinardia delicatula is a cosmopolitan species that dominates seasonal blooms in the English Channel and the North Sea. Several eukaryotic parasites are known to induce the mortality of this key-stone species. Here, we report the isolation and the characterization of the first viruses that infect G. delicatula. Viruses were isolated from the Western English Channel (SOMLIT-ASTAN station) during the late summer bloom decline of G. delicatula. A combination of laboratory approaches revealed that these lytic viruses (GdelRNAV) are small untailed particles of 35-38 nm in diameter that replicated in the host cytoplasm where both unordered particles and crystalline arrays were formed. GdelRNAV displayed a linear single-stranded RNA genome of ~9 kb, including two open reading frames encoding for replication and structural polyproteins. Phylogenetic relationships based on the RNA-dependent-RNA-polymerase gene marker showed that GdelRNAV were new members of the Bacillarnavirus, a monophyletic genus belonging to the order Picornavirales. GdelRNAV were specific to several strains of G. delicatula, they were produced rapidly (< 12h) and in numbers (9.34 x 104 virions per host cell). We recorded a substantial delay (72 h) between virions release and host cell lysis. Our analysis points to variable viral susceptibilities of the host during the early exponential growth phase. Interestingly, we consistently failed to isolate viruses during spring and early summer while G. delicatula developed rapid and massive blooms. While our study suggests that viruses do contribute to the decline of G. delicatula late summer bloom, they may not be the primary mortality agents during the remaining blooms at SOMLIT-ASTAN. Future studies should focus on the relative contribution of the viral and eukaryotic pathogens to the control of Guinardia blooms to understand the fate of these prominent organisms in marine systems.
Project description:The dataset represents the proteome analysis of six sampling dates during the phytoplankton bloom at the island of Helgoland in the North Sea at the long term research station ‘Kabeltonne’ (54° 11' 17.88'' N, 7° 54' 0'' E) in 2016.
Project description:The dataset represents the proteome analysis of 15 sampling dates during the phytoplankton bloom in the Helgoland Roads in the North Sea at the long-term research station ‘Kabeltonne’ (54°11'N 7°54'E, DEIMS.ID https://deims.org/1e96ef9b-0915-4661-849f-b3a72f5aa9b1) in 2020.
Project description:The dataset represents the proteome analysis of 7 sampling dates during the phytoplankton bloom in the Helgoland Roads in the North Sea at the long-term research station ‘Kabeltonne’ (54°11'N 7°54'E, DEIMS.ID https://deims.org/1e96ef9b-0915-4661-849f-b3a72f5aa9b1) in 2018.
Project description:Laminarin is a major storage polysaccharide in phytoplankton and an important carbon and energy source for marine microbes. How microbes compete for this labile polysaccharide in nature remains unclear. Here we investigated metaproteomes and metagenomes of bacterioplankton during four consecutive algal blooms in the North Sea to determine key laminarin consumers. We identified two specialized laminarin degraders of the Bacteroidetes group, which reached high abundances year after year. We found that these genomically streamlined bacteria of the genus Formosa have an expanded set of laminarin hydrolases, sensors and transporters that belonged to the most abundant proteins in the blooms. The respective genes are organized in three polysaccharide utilization loci. Proteomic and biochemical analyses revealed surface tethered enzymes and a laminarinase recombined with a membrane-spanning transporter, which act as a disassembly line and efficiently integrate substrate degradation and uptake in the highly diffusive, aquatic environment. We also show that the bloom bacteria couple laminarin utilization with uptake of cellular building blocks such as amino acids. This study suggests that in addition to genome reduction, enzyme fusions, transporter and enzyme expansion also the tight coupling of the carbon and nitrogen uptake make Formosa spp. efficient laminarin utilizers.
Project description:Marine phytoplankton are a diverse group of photoautotrophic organisms and key mediators in the global carbon cycle. Phytoplankton physiology and biomass accumulation are closely tied to mixed layer depth, but the intracellular metabolic pathways activated in response to changing mixed layer depths remain unexplored. Here, metatranscriptomics was used to characterize the phytoplankton community response to a mixed layer shallowing from 233 meters to 5 meters over the course of two days during the late spring in the Northwest Atlantic. Most phytoplankton genera downregulated core photosynthesis, carbon storage, and carbon fixation genes as the system transitioned from a deep to a shallow mixed layer and shifted towards catabolism of stored carbon ic pathways supportive of rapid cell growth. In contrast, phytoplankton genera exhibited divergent transcriptional strategies for photosystem light harvesting complex genes during this transition. Active infection, taken as the ratio of virus to host transcripts, increased in the Bacillariophyta (diatom) phylum and decreased in the Chlorophyta (green algae) phylum upon mixed layer shallowing. A conceptual model is proposed to provide ecophysiological context for our findings, in which light limitation during deep mixing induces populations into a transcriptional state which maximizes interrupts the oscillating levels of transcripts related to photosynthesis, carbon storage, and carbon fixation found in shallow mixed layers with relatively higher growth rates. We propose that upon sensing high light levels during mixed layer shallowing, phytoplankton resume diel oscillation of core sets of genes enabling photoprotection, biosynthesis and cell replication. Our findings highlight the shared and unique transcriptional response strategies within phytoplankton communities acclimating to the dynamic light environment associated with transient deep mixing and shallowing events during the annual North Atlantic bloom.