Series 4: Aggregation of Thalassiosira weissflogii as a function of pCO2, temperature and bacteria

The Series 4 Experiment, Aggregation of Thalassiosira weissflogii as a function of pCO2, temperature and bacteria, is made up of 2 phases. The Acclimatisation Phase and the Aggregation Phase. The Acclimatisation Phase has two components – The Carbonate System data and the Cell Counts Data. The Aggregation Phase also has two components – The Carbonate System + TEP data and the Sinking Velocity data. Note: For a complete list of measurements, refer to the supplemental document ' Series4_Field_names.pdf' .Increasing Transparent Exopolymer Particle (TEP) formation during diatom blooms as a result of elevated temperature and pCO2 have been suggested to result in enhanced aggregation and carbon flux, therewith potentially increasing the sequestration of carbon by the ocean. We present experimental results on TEP and aggregate formation by Thalassiosira weissflogii (diatom) in the presence or absence of bacteria under two temperature and three pCO2 scenarios. During the aggregation phase of the experiment TEP formation was elevated at the higher temperature (20ºC vs. 15ºC), as predicted. However, in contrast to expectations based on the established relationship between TEP and aggregation, aggregation rates and sinking velocity of aggregates were depressed in warmer treatments, especially under ocean acidification conditions. If our experimental findings can be extrapolated to natural conditions, they would imply a reduction in carbon flux and potentially reduced carbon sequestration after diatoms blooms in the future ocean.This research was supported by NSF Grant: OCE-09267112014-10-0

Aggregation and Sedimentation of Thalassiosira weissflogii (diatom) in a Warmer and More Acidified Future Ocean

© The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS One 9 (2014): e112379, doi:10.1575/1912/6845.Increasing Transparent Exopolymer Particle (TEP) formation during diatom blooms as a result of elevated temperature and pCO2 have been suggested to result in enhanced aggregation and carbon flux, therewith potentially increasing the sequestration of carbon by the ocean. We present experimental results on TEP and aggregate formation by Thalassiosira weissflogii (diatom) in the presence or absence of bacteria under two temperature and three pCO2 scenarios. During the aggregation phase of the experiment TEP formation was elevated at the higher temperature (20°C vs. 15°C), as predicted. However, in contrast to expectations based on the established relationship between TEP and aggregation, aggregation rates and sinking velocity of aggregates were depressed in warmer treatments, especially under ocean acidification conditions. If our experimental findings can be extrapolated to natural conditions, they would imply a reduction in carbon flux and potentially reduced carbon sequestration after diatom blooms in the future ocean.This work was supported by National Science Foundation grants OCE-0926711 & OCE-1041038 to UP and Helmholtz Graduate School for Polar and Marine Research and Jacobs University Bremen to SS

Defensins knowledgebase: a manually curated database and information source focused on the defensins family of antimicrobial peptides

The defensins knowledgebase is a manually curated database and information source focused on the defensin family of antimicrobial peptides. The current version of the database holds a comprehensive collection of over 350 defensin records each containing sequence, structure and activity information. A web-based interface provides access to the information and allows for text-based searching on the data fields. In addition, the website presents information on patents, grants, research laboratories and scientists, clinical studies and commercial entities pertaining to defensins. With the rapidly increasing interest in defensins, we hope that the knowledgebase will prove to be a valuable resource in the field of antimicrobial peptide research. The defensins knowledgebase is available at

Complete genome sequence of Marinobacter adhaerens type strain (HP15), a diatom-interacting marine microorganism

Revista Open Access. Artículo con licencia Creative Commons Attribution. -- 11 páginas, 4 figuras, 4 tablas.Marinobacter adhaerens HP15 is the type strain of a newly identified marine species, which is phylogenetically related to M. flavimaris, M. algicola, and M. aquaeolei. It is of special interest for research on marine aggregate formation because it showed specific attachment to diatom cells. In vitro it led to exopolymer formation and aggregation of these algal cells to form marine snow particles. M. adhaerens HP15 is a free-living, motile, rod-shaped, Gram-negative Gammaproteobacterium, which was originally isolated from marine particles sampled in the German Wadden Sea. M. adhaerens HP15 grows heterotrophically on various media, is easy to access genetically, and serves as a model organism to investigate the cellular and molecular interactions with the diatom Thalassiosira weissflogii. Here we describe the complete and annotated genome sequence of M. adhaerens HP15 as well as some details on flagella-associated genes. M. adhaerens HP15 possesses three replicons; the chromosome comprises 4,422,725 bp and codes for 4,180 protein-coding genes, 51 tRNAs and three rRNA operons, while the two circular plasmids are ~187 kb and ~42 kb in size and contain 178 and 52 protein-coding genes, respectively.Peer reviewe

Comparison of average TEP production (µg GXeq. L⁻¹) and aggregation, as measured by total aggregate volume (Agg. Vol.), combining treatments with the same temperature, carbonate conditions, or state of axenicity, respectively.

<p>N =  number of treatments, each in duplicate.</p><p>*: averages significantly (p<0.05) different from each other, paired t-test.</p><p>Comparison of average TEP production (µg GXeq. L⁻¹) and aggregation, as measured by total aggregate volume (Agg. Vol.), combining treatments with the same temperature, carbonate conditions, or state of axenicity, respectively.</p

Effect of autoclaving on the carbonate chemistry of seawater.

<p>Effect of autoclaving on the carbonate chemistry of seawater.</p

Production of Transparent Exopolymer Particles (TEP) during the incubations in all treatments, calculated as net change during the 96 hrs. experiment, and errors calculated using error propagation.

<p>Production of Transparent Exopolymer Particles (TEP) during the incubations in all treatments, calculated as net change during the 96 hrs. experiment, and errors calculated using error propagation.</p

Exponential growth of <i>T. weissflogii</i> and pH range during the acclimatization phase.

<p>Exponential growth of <i>T. weissflogii</i> and pH range during the acclimatization phase.</p

Design of multifactorial experiment with 12 treatments testing aggregation of the diatom <i>T. weissflogii</i> in the presence or absence of bacteria at two temperatures and three <i>p</i>CO₂ scenarios.

<p>Xenic treatments contained the bacterium <i>M. adhaerens</i> HP15. Each treatment was prepared in triplicate; one replicate was harvested initially (t = 0) and two after 96 hr. incubation on roller tables in the dark. See text for specifics on <i>p</i>CO₂ treatments. Ax  =  axenic, HP  =  <i>M. adhaerens</i> HP15 added, Am  =  Ambient, F1  =  Future 1, F2  =  Future 2.</p><p>Design of multifactorial experiment with 12 treatments testing aggregation of the diatom <i>T. weissflogii</i> in the presence or absence of bacteria at two temperatures and three <i>p</i>CO₂ scenarios.</p

Initial and final <i>p</i>CO₂ during the incubations at 15°C and 20°C.

<p>Initial and final <i>p</i>CO₂ during the incubations at 15°C and 20°C.</p