Project description:Application of genome-scale 'omics approaches to dissect subcellular pathways and regulatory networks governing the fast-growing response of Synechococcus sp. PCC 7002 response to variable irradience levels. We employed controlled cultivation and next-generation sequencing technology to identify transcriptional responses of euryhaline unicellular cyanobacterium Synechococcus sp. PCC 7002 grown under steady state conditions at six irradiance levels ranging from 33 to 760 µmol photons m-2 sec-1.
Project description:Application of genome-scale 'omics approaches to dissect subcellular pathways and regulatory networks governing the fast-growing response of Synechococcus sp. PCC 7002 response to variable irradience levels.
Project description:Cyanobacteria are valuable organisms for studying the physiology of photosynthesis and carbon fixation as well as metabolic engineering for the production of fuels and chemicals. This work describes a novel counter selection method for the cyanobacterium Synechococcus sp. PCC 7002 based on organic acid toxicity. The organic acids acrylate, 3-hydroxypropionate, and propionate were shown to be inhibitory towards PCC 7002 and other cyanobacteria at low concentrations. Inhibition was overcome by a loss of function mutation in the gene acsA. Loss of AcsA function was used as a basis for an acrylate counter selection method. DNA fragments of interest were inserted into the acsA locus and strains harboring the insertion were isolated on selective medium containing acrylate. This methodology was also used to introduce DNA fragments into a pseudogene, glpK. Application of this method will allow for more advanced genetics and engineering studies in PCC 7002 including the construction of markerless gene deletions and insertions. The acrylate counter-selection could be applied to other cyanobacterial species where AcsA activity confers acrylate sensitivity (e.g. Synechocystis sp. PCC 6803).
Project description:Cyanobacteria are valuable organisms for studying the physiology of photosynthesis and carbon fixation as well as metabolic engineering for the production of fuels and chemicals. This work describes a novel counter selection method for the cyanobacterium Synechococcus sp. PCC 7002 based on organic acid toxicity. The organic acids acrylate, 3-hydroxypropionate, and propionate were shown to be inhibitory towards PCC 7002 and other cyanobacteria at low concentrations. Inhibition was overcome by a loss of function mutation in the gene acsA. Loss of AcsA function was used as a basis for an acrylate counter selection method. DNA fragments of interest were inserted into the acsA locus and strains harboring the insertion were isolated on selective medium containing acrylate. This methodology was also used to introduce DNA fragments into a pseudogene, glpK. Application of this method will allow for more advanced genetics and engineering studies in PCC 7002 including the construction of markerless gene deletions and insertions. The acrylate counter-selection could be applied to other cyanobacterial species where AcsA activity confers acrylate sensitivity (e.g. Synechocystis sp. PCC 6803). Cultures were grown in medium modified with 5mM acrylic acid at pH 8 and compared to cultures grown in unmodified medium. Samples were processed in duplicate.
Project description:Cyanobacteria fix atmospheric CO2 to biomass and through metabolic engineering can also act as photosynthetic cell factories for sustainable productions of fuels and chemicals. The Calvin cycle is the primary pathway for CO2 fixation in cyanobacteria, algae and C3 plants, and several studies have shown that overexpression of a cyanobacterial Calvin cycle enzyme, bifunctional sedoheptulose-1,7-bisphosphatase/fructose-1,6-bisphosphatase (hereafter BiBPase), enhances CO2 fixation in both plants and algae, although its impact on cyanobacteria has not yet been rigorously studied. Here, we show that overexpression of BiBPase enhanced growth, cell size, and photosynthetic O2 evolution of the cyanobacterium Synechococcus sp. PCC 7002 in an environment with elevated CO2 concentration. Biochemical analysis, immunodetection, and proteomic analysis revealed that overexpression of BiBPase considerably elevated the cellular activities of two rate-limiting enzymes in the Calvin cycle, namely ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and aldolase, while it repressed several enzymes involved in the respiratory carbon metabolism (e.g. glycolysis and the oxidative pentose phosphate pathway) including glucose-6-phosphate dehydrogenase. Concomitantly, the content of glycogen was significantly reduced while the extracellular carbohydrate content increased. These results indicate that overexpression of BiBPase leads to global reprogramming of carbon metabolism in Synechococcus sp. PCC 7002, promoting photosynthetic carbon fixation and repressing the respiratory carbon catabolism, while altering carbohydrate partitioning.
Project description:RNase III is a ribonucleases that recognizes and cleaves double-stranded RNA. RNase III has been known be involved in rRNA processing, but has many additional roles controlling both expression and RNA turnover of specific messages. Many organisms have just one RNase III while some have both a full length RNase III and a mini-III that lacks the double-stranded RNA binding domain. The cyanobacteria Synechococcus sp. PCC 7002 has three homologs of RNase III that are unessential even when deleted in combination. We were interested what coding regions these RNase III enzymes were influencing and if they had redundant or distinct specificities. To address these questions we collected samples for RNA-sequencing from WT, the single, double, and triple RNase III mutants in triplicate. Approximately 20% of genes were differentially expressed in various mutants with some operons and regulons showing complex changes in expression levels between mutants. We describe the role of two RNase III’s in 23S rRNA maturation, and show how the third is involved in copy number regulation of one of the six plasmids (pAQ3). Purified enzymes were capable of cleaving some E. coli RNase III target sequences, highlighting the remarkably conserved substrate specificity between organisms yet complex regulation of gene expression.
Project description:Like many other organisms, cyanobacteria exhibit rhythmic gene expression with a period length of 24 hours to adapt to daily environmental changes. In the model organism Synechococcus elongatus PCC 7942 the central oscillator consists of three proteins: KaiA, KaiB and KaiC and utilizes the histidine kinase SasA and its response regulator RpaA as output-signaling pathway. Synechocystis sp. PCC 6803 contains two additional homologs of the kaiB and kaiC genes. Here we demonstrate that RpaA interacts with the core oscillator KaiAB1C1 of Synechocystis sp. PCC 6803 via SasA, similar to Synechococcus elongatus PCC 7942. However, interaction with the additional Kai homologs was not detected, suggesting different signal transduction components for the clock homologs. Inactivation of rpaA in Synechocystis sp. PCC 6803, lead to reduced viability of the mutant in light-dark cycles that aggravated under mixotrophic growth conditions. Chemoheterotrophic growth in the dark was abolished completely. In accordance, transcriptomic data revealed that RpaA is involved in the regulation of genes related to CO2‑acclimation and carbon metabolism under diurnal light conditions. Further, our results indicate that RpaA functions in the posttranslational regulation of glycogen metabolism as well, and a potential link between the circadian clock and motility was identified.