Unknown,Transcriptomics,Genomics,Proteomics

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Diel growth of Thalassiosira pseudonana

ABSTRACT: Transcript levels of all T. pseudonana genes was measured every twelve hours throughout the batch (non-chemostatic) growth of axenic cells grown in large glass bioreactors on a 12hr:12hr dark:light cycle for five days. The data were analyzed to reveal the physiological and regulatory changes that recurred in this diatom when transitioning between dark and light conditions, as well as from exponential phase to stationary, nutrient limited conditions. The longitudinal experiment was performed with two replicates, at 400 and 800ppm CO2. Two growth experiments were conducted, with 10 and 9 longitudinal samples collected from each experiment, respectively. Two-color arrays were used with dye flips for labeling. A common internal reference sample was used for one channel on each array. Expression changes for longitudinal analysis were calculated as the difference from the mean log2 expression ratio for each to the common reference sample, for each gene, over all samples within an experiment. For the analysis of diel states in T. pseudonana, samples from the two series were matched according to the time from innoculation, and divided into four classes: dawn samples (taken at the end of each dark phase), dusk samples (taken at the end of each light phase), exponential samples (the first five samples in each series prior to a drop in growth rate on Day 3), and stationary samples (all samples including following the drop in growth rate on Day 3).

ORGANISM(S): Thalassiosira pseudonana CCMP1335

SUBMITTER: Justin Ashworth

PROVIDER: E-GEOD-45252 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Here, we examined the ramifications of between-species diversity by documenting the transcriptional response of three marine diatoms - Thalassiosira pseudonana, Fragilariopsis cylindrus, and Pseudo-nitzschia multiseries - to the onset of nitrate limitation of growth, a common limiting nutrient in the ocean. Less than 5% of orthologous genes, shared across the three diatoms, displayed the same transcriptional responses across species when growth was limited by nitrate availability. Orthologs, such as those involved in nitrogen uptake and assimilation, as well as carbon metabolism, were differently expressed across the three species. The two pennate diatoms, F. cylindrus and P. multiseries, shared 3,839 clusters without orthologs in the genome of the centric diatom T. pseudonana. A majority of these pennate-clustered genes, as well as the non-orthologous genes in each species, had minimal annotation information, but were often significantly differentially expressed under nitrate limitation, indicating their potential importance in the response to nitrogen availability. Despite these variations in the specific transcriptional response of each diatom, overall transcriptional patterns suggested that all three diatoms displayed a common physiological response to nitrate limitation that consisted of a general reduction in carbon fixation and carbohydrate and fatty acid metabolism and an increase in nitrogen recycling. Transcriptomes were collected for diatom cultures harvested at the onset of stationary phase in low nitrate media (55 M-NM-<M NaNO3, 212 M-NM-<M Na2SiO3, 72.4 M-NM-<M NaH2PO4) or during mid-exponential growth in nutrient-replete media (882 M-NM-<M NaNO3, 106 M-NM-<M Na2SiO3, 36.2 M-NM-<M NaH2PO4) in artificial seawater, maintaining three biological replicates per condition and per diatom (N=18). The SOLiD sequencer (version 4) was used to generate the transcriptomes and the SEAStAR software package was used to process the SOLiD reads and to calculate gene counts. Pooled counts for the nitrate-limited treatment were normalized to pooled counts for the nutrient-replete M-bM-^@M-^\controlM-bM-^@M-^] treatment to generate log fold changes in gene transcription using the R software package edgeR from Bioconductor.

Project description:The foodborne pathogen Listeria monocytogenes experiences osmotic stress in many habitats, including foods and the gastrointestinal tract of the host. While osmotic stress induced changes in expression have been investigated for specific genes, identifying and understanding genome-wide temporal changes in the transcriptome due to salt stress will provide insights into how this pathogen adapts to and survives this stress, leading to development of new intervention strategies. To determine the short-term and long-term responses to salt stress, we exposed exponential phase cells of L. monocytogenes H7858 to 6% NaCl in Brain Heart Infusion (BHI) broth at 7°C and 37°C and extracted RNA after 2.5%, 5%, 10%, and 20% of lag phase and during exponential growth in BHI + 6% NaCl, and evaluated temporal changes in transcript levels with microarrays. The temperature dependent short-term response to salt stress included a significant increase in transcript levels of the alternative sigma factor σB, with maximum expression at 2.5-5% of lag phase at 37°C, and at 20% of lag phase at 7°C. Transcript levels of genes known to be regulated by σB, including inlAB, opuCA, glpFK, and gadBC, were significantly upregulated at the same relative time points as σB As indicated by significantly elevated transcript levels during exponential growth in BHI + 6% NaCl, genes encoding proteins involved in purine and pyrimidine synthesis and amino acid biosynthesis are part of the long-term response to salt stress at 37°C. Transcript levels of virulence genes plcA, mpl, actA, and plcB were also significantly upregulated during exponential growth under salt stress at 37°C. Genes encoding proteins involved in protein degradation and stability and cell membrane modifications are part of the long-term response to salt stress at 7°C. Overall, an initial alteration in the transcriptome occurs, decreasing transcript levels of genes encoding proteins involved in energy conversion and metabolism, while increasing transcript levels of those involved in the stress response controlled by σB, followed by a long-term response, including increased expression of genes encoding compatible solute transporters and general stress proteins, facilitating growth under salt stress. A reference design was used to analyze gene expression differences. Exponential phase cultures at 37C and at 7C were used as a reference for salt stressed samples at each temperature. Salt stressed samples from the same relative time point were compared across temperatures. 4 biological replicates were tested for each comparison.

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Diel growth of Thalassiosira pseudonana

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