Project description:Here, we treated the model cyanobacterium Synechococcus elongatus PCC7942 with streptomycin, which selectively binds to bacterial ribosomes, at a concentration of 50 µg/mL and performed transcriptome analysis using RNA sequencing. In addition to antibiotic stress, we treated salt stress (0.4 M NaCl) and performed RNA sequencing analysis.
Project description:The circadian clock of the cyanobacterium Synechococcus elongatus PCC 7942 drives oscillations in global mRNA abundances with 24 hour periodicity under constant light conditions. The transcription factor RpaA, a circadian clock-regulated transcription factor, controls the timing of circadian gene expression, but the mechanisms underlying this control are not well understood. Here we show that four RpaA-dependent sigma factors – RpoD2, RpoD6, RpoD5, and SigF2 – are sequentially activated downstream of active RpaA and are required for proper expression of circadian mRNAs. We find that RpoD6, RpoD5, and SigF2 exhibit circadian oscillations with different timing relative to each other at the level of mRNA expression and protein abundance. By measuring global gene expression in strains modified to individually lack rpoD2, rpoD6, rpoD5, and sigF2 we identify how expression of circadian mRNAs – including sigma factor mRNAs – is altered in the absence of each sigma factor. Broadly, our findings suggest that a single transcription factor, RpaA, is sufficient to generate complex circadian expression patterns in part by regulating an interdependent sigma factor cascade.
Project description:Phytoplankton are known to release organic compounds that fuel secondary production by heterotrophic bacteria. Here we show that an abundant marine cyanobacterium, Synechococcus elongatus, contributes a variety of nitrogen-rich and sulfur-containing compounds to dissolved organic matter. A combination of targeted and untargeted metabolomics and genomic tools was used to characterize the intracellular and extracellular metabolites of S. elongatus. Aromatic compounds such as 4-hydroxybenzoic acid and phenylalanine, as well as nucleosides (e.g., thymidine, 5’-methylthioadenosine, xanthosine), the organosulfur compound 3-mercaptopropionate, and the plant auxin indole 3-acetic acid, were detected in the extracellular metabolites at multiple time points during the growth of S. elongatus. Further, the amino acid kynurenine was found to accumulate in the media even though it was not included in the predicted metabolome of S. elongatus. This suggests that not all metabolites produced by an organism can be predicted from its genome sequence. Some metabolites may be products of non-enzymatic reactions and are likely excreted into the environment as waste. The compounds described herein provide excellent targets for quantitative analysis in field settings to assess the source and lability of dissolved organic matter in situ.
