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:Sequencing the metatranscriptome can provide information about the response of organisms to varying environmental conditions. We present a methodology for obtaining random whole-community mRNA from a complex microbial assemblage using Pyrosequencing. The metatranscriptome had, with minimum contamination by ribosomal RNA, significant coverage of abundant transcripts, and included significantly more potentially novel proteins than in the metagenome. Keywords: metatranscriptome, mesocosm, ocean acidification This experiment is part of a much larger experiment. We have produced 4 454 metatranscriptomic datasets and 6 454 metagenomic datasets. These were derived from 4 samples. The experiment is an ocean acidification mesocosm set up in a Norwegian Fjord in 2006. We suspended 6 bags containing 11,000 L of sea water in a Coastal Fjord and then we bubbled CO2 through three of these bags to simulate ocean acidification conditions in the year 2100. The other three bags were bubbled with air. We then induced a phytoplankton bloom in all six bags and took measurements and performed analyses of phytoplankton, bacterioplankton and physiochemical characteristics over a 22 day period. We took water samples from the peak of the phytoplankton bloom and following the decline of the phytoplankton bloom to analyses using 454 metagenomics and 454 metatranscriptomics. Day 1, High CO2 Bag and Day 1, Present Day Bag, refer to the metatranscriptomes from the peak of the bloom. Day 2, High CO2 Bag and Day 2, Present Day Bag, refer to the metatranscriptomes following the decline of the bloom. Obviously High CO2 refers to the ocean acidification mesocosm and Present Day refers to the control mesocosm. Raw data for both the metagenomic and metatranscriptomic components are available at NCBI's Short Read Archive at ftp://ftp.ncbi.nlm.nih.gov/sra/Studies/SRP000/SRP000101
Project description:Seasonal changes in nitrogen assimilation have been studied in the western English Channel by sampling at approximately weekly intervals for 12 months. Nitrate concentrations showed strong seasonal variations. Available nitrogen in the winter was dominated by nitrate but this was close to limit of detection from May to September, after the spring phytoplankton bloom. 15N uptake experiments showed that nitrate was the nitrogen source for the spring phytoplankton bloom but regenerated nitrogen supported phytoplankton productivity throughout the summer. The average annual f ratio was 0.35, which demonstrated the importance of ammonia regeneration in this dynamic temperate region. Nitrogen uptake rate measurements were related to the phytoplankton responsible by assessing the relative abundance of nitrate reductase (NR) genes and the expression of NR among eukaryotic phytoplankton. Strong signals were detected from NR sequences that are not associated with known phylotypes or cultures. NR sequences from the diatom Phaeodactylum tricornutum were highly represented in gene abundance and expression, and were significantly correlated with f ratio. The results demonstrate that analysis of functional genes provides additional information, and may be able to give better indications of which phytoplankton species are responsible for the observed seasonal changes in f ratio than microscopic phytoplankton identification. NR gene diversity from seawater (two replicates of 16 blocks per array, 8 replicate features per probe, duplicate arrays for some samples) The arrays contain three sets of probes for different applications (rbcL and nitrate reductase (NR) from phytoplankton, and amoA from ammonia oxidizing bacteria). The paper to which this submission relates, and the experiments reported in it, used only the NR probe set.
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.
Project description:Marine snow plays a central role in carbon cycling. It consists of organic particles and particle-associated (PA) microbMarine snow plays a central role in carbon cycling. It consists of organic particles and particle-associated (PA) microbial communities that are embedded in a sugary matrix. Metaproteomic analysis offers the unique opportunity to gain unprecedented insight into the microbial community composition and biomolecular activity of environmental samples. In order to realize this potential for marine PA microbial communities, new methods of protein extraction must be developed. In this study, we used 1D-SDS-PAGEs and LC-MS/MS to compare the efficiency of six established protein extraction protocols for their applicability of metaproteomic analyses of the PA microbial community in the North Sea. A combination of SDS-buffer extraction and bead beating resulted in the greatest number of identified protein groups. As expected, a metagenomic database of the same environmental sample increased the number of protein identification by approximately 50%. To demonstrate the application of our established protocol, particulate bacterioplankton samples collected during spring phytoplankton bloom in 2009 near the island Helgoland, were analysed by a GeLC-MS/MS-based metaproteomic approach. Our results indicated that there are only slight differences in the taxonomical distribution between free-living (FL) and PA bacteria but that the abundance of protein groups involved in polysaccharide degradation, motility and particle specific stress (oxygen limitation, nutrient limitation, heavy metal stress) is higher in the PA fractions. ial communities that are embedded in a sugary matrix. Metaproteomic analysis offers the unique opportunity to gain unprecedented insight into the microbial community composition and biomolecular activity of environmental samples. In order to realize this potential for marine PA microbial communities, new methods of protein extraction must be developed. In this study, we used 1D-SDS-PAGEs and LC-MS/MS to compare the efficiency of six established protein extraction protocols for the their applicability of metaproteomic analyses of the PA microbial community in the North Sea. A combination of SDS-buffer extraction and bead beating resulted in the greatest number of identified protein groups. As expected, a metagenomic database of the same environmental sample increased the number of protein identification by approximately 50%. To demonstrate the application of our established protocol, particulate bacterioplankton samples collected during spring phytoplankton bloom in 2009 near the island Helgoland, were analysed by a GeLC-MS/MS-based metaproteomic approach. Our results indicated that there are only slight differences in the taxonomical distribution between free-living (FL) and PA bacteria but that the abundance of protein groups involved in polysaccharide degradation, motility and particle specific stress (oxygen limitation, nutrient limitation, heavy metal stress) is higher in the PA fractions.