RNA-seq analysis of recombinant Synechocystis sp. 6803 provides important insights for understanding polyhydroxyalkanoate production in cyanobacteria under photoautotrophic conditions
ABSTRACT: The direct photosynthetic production of polyhydroxyalkanoate in cyanobacteria was improved by increasing carbon flux to biosynthetic pathway and introducing enzyme with higher activity. To understand the global transcriptional changes under photoautotrophic PHA biosynthesis conditions, RNA-seq analysis was performed. Transcriptomes of recombinant Synechocystis sp. with different PHA-producing potential (three strains, two biological replicates for each strain) were analyzed.
Project description:Ethylene is a gaseous signal sensed by plants and bacteria. Heterologous expression of the ethylene-forming enzyme (EFE) from Pseudomonas syringae in cyanobacteria leads to the production of ethylene under photoautotrophic conditions. The recent characterization of an ethylene responsive signaling pathway affecting phototaxis in the cyanobacterium Synechocystis sp. PCC 6803 implies that biotechnologically relevant ethylene synthesis may induce regulatory processes which are not related to changes in the metabolism. Here we provide data that endogenously produced ethylene accelerates movement of cells towards light. Microarray analysis demonstrates that ethylene deactivates transcription from the csiR1/lsiR promoter which is under control of the two-component system consisting of the ethylene and UV-A-sensing histidine kinase UirS and the DNA-binding response regulator UirR. Surprisingly, only very few other transcriptional changes were detected in the microarray analysis providing no direct hints to possible bottlenecks in phototrophic ethylene production. Overall design: We performed whole-genome transcript profiling of an ethylene producing strain of Synechocystis sp. PCC 6803.
Project description:The 6S RNA is a global transcriptional riboregulator, which is exceptionally widespread among most bacterial phyla. While its role is already well-characterized in heterotrophic bacteria, we subjected a cyanobacterial homolog to functional analysis, thereby extending the scope of 6S RNA action to the special challenges of photoautotrophic lifestyles. This study reveals 6S RNA as an integral part of the cellular response of Synechocystis sp. PCC 6803 to changing nitrogen availability. Physiological characterization of a 6S RNA deletion strain (ΔssaA) demonstrates a delay in the recovery from nitrogen starvation. Significantly decelerated phycobilisome reassembly and glycogen degradation is accompanied with reduced photosynthetic activity compared to the wild type. Transcriptome profiling further revealed that predominantly genes encoding components of both photosystems, ATP synthase and the phycobilisomes were negatively affected in the ΔssaA mutant. In vivo pull-down studies of the RNA polymerase complex further indicate a promoting effect of 6S RNA on the recruitment of the cyanobacterial housekeeping sigma factor SigA, concurrently supporting dissociation of group II sigma factors during recovery from nitrogen starvation. According to these results, 6S RNA supports a rapid adaptation to changing nitrogen conditions by regulating the switch from group II sigma factors SigB / SigC to SigE / SigA dependent transcription. We performed microarray analysis of total RNA from wild-type and ∆ssaA cultures that were starved for nitrogen for seven days and recovered over a period of 48 hours. Sampling time points were t1 = 1h +N, t2 = 4h +N and t3 = 22h +N after nitrogen recovery. Samples were taken in biological replicates.
Project description:Cyanobacteria are photoautotrophic prokaryotes with a plant-like photosynthetic machinery. Besides being able to grow photoautotrophically, some cyanobacteria are also capable to grow photoheterotrophically, where they use reduced organic compounds as carbon source, or even completely heterotrophically by using reduced organic compounds as carbon and energy source. The well characterized cyanobacterium Synechocystis sp. PCC 6803 can grow in darkness under light-activated heterotrophic growth (LAHG) conditions by using glucose as carbon and energy source. In the present work, we combined pre-fractioning of Synechocystis cellular membranes with a global proteome and lipidome analysis, to shift the analytical focus towards the rearrangement of the internal thylakoid membrane system observed in Synechocystis cells under LAHG conditions.
Project description:Cyanobacteria are phototrophic prokaryotes that can convert inorganic carbon as CO2 into organic carbon compounds at the expense of light energy. In addition, they need only a few inorganic nutrients and can be cultivated in high densities using non-arable land and seawater. This features qualified cyanobacteria as attractive organisms for the production of third generation biofuels as part of the development of future CO2-neutral energy production. Synechocystis sp. PCC 6803 represents one of the most widely used cyanobacterial model strains. On the basis of its available genome sequence and genetic tools, many strains of Synechocystis have been generated that produce different biotechnological products. Efficient isoprene production is an attractive goal, since this compound represents not only an energy-rich biofuel but is also used as chemical feedstock. Here, we report on our attempts to generate isoprene-producing strains of Synechocystis. The cDNA of a codon-optimized plant isoprene synthase (IspS) was cloned under the control of different Synechocystis promoters, which ensure strong constitutive or light-regulated ispS expression. The expression of the ispS gene was quantified by qPCR, whereas the amount of isoprene was quantified using GC-MS. Incubation of our strains at different salt conditions had marked impact on the isoprene production rates. Under low salt conditions, a good correlation was found between ispS expression and isoprene production rate. However, the cultivation of isoprene production strains under salt-supplemented conditions decreased isoprene production despite the fact that ispS expression was salt-stimulated. The characterization of the metabolome of isoprene producing strains indicated that isoprene production might be limited by insufficient precursor levels. Our isoprene production rates under low salt conditions were 2 - 6.5times higher compared to the previous report of Lindberg et al. (2010). These results can be used to guide future attempts establishing the isoprene production with cyanobacterial host systems. Overall design: We monitored gene expression of an Synechocystis PCC6083 WT strain in comparison with the isoprene producing strain #642. Sample were done in biological replicates
Project description:Carbohydrate metabolism is a tightly regulated process in photosynthetic organisms. The ability to utilize glucose for growth and to regulate storage carbohydrate (i.e. glycogen) metabolisms requires a number of regulatory elements. In the cyanobacterium Synechocystis sp. PCC 6803, the photomixotrophic growth protein A (PmgA), a putative serine/threonine kinase, is involved in governing these abilities; however its downstream regulatory elements are not well studied. Here a genome-wide microarray analysis of a ∆pmgA strain revealed altered transcript levels of several non-coding RNAs, among them Ncr0700 was the most strongly reduced transcript. Generally, Ncr0700 is highly conserved among cyanobacteria. In Synechocystis its expression is light-dependent, i.e. the abundance is reciprocal to the light intensity. Compared to WT and similar to a ΔpmgA mutant, a ∆ncr0700 deletion strain showed a ~2 fold increase in glycogen content under photoautotrophic conditions. Under these conditions ∆ncr0700 grew similarly to the wild type; in contrast its growth was arrested after a shift to photomixotrophic conditions. Ectopic expression of Ncr0700 in ∆ncr0700 as well as ∆pmgA restored both the glycogen and photomixotrophic growth to the wild type levels. These results indicate that Ncr0700 plays a role in regulation of carbohydrate metabolism, acts downstream of PmgA and therefore is renamed here to PmgR1 for photomixotrophic growth RNA 1. Overall design: We analyzed gene expression in Synechocystis sp. PCC 6803 WT as well as a ∆pmgA (sll1968) mutant grown at 50 μmol photons m–2 s–1 at 30°C with continuous bubbling with air supplemented with 3% (v/v) CO2. Three biological replicates were analyzed for ΔpmgA and compared with 2 replicate cultures of WT.
Project description:Global gene expression of Synechocystis sp. PCC 6803 encapsulated in silica gel was examined by microarray analysis. Cultures were encapsulated in gels derived from aqueous precursors and gels derived from alkoxide precursors and incubated under constant light for 24 hours prior to RNA extraction. Cultures suspended in liquid media were also exposed to 500 mM salt stress and incubated under identical conditions, for comparison purposes. The expression of 414 genes was significantly altered by encapsulation in aqueous-derived gels (fold change >/= 1.5 and P-value < 0.01), the expression of 1143 genes were significantly altered by encapsulation in alkoxide derived gels, and only 243 genes were common to both encapsulation chemistries. Additional qRT-PCR analyses of four select genes; ggpS, cpcG2, slr5055, and sll5057, confirmed microarray results. These results illustrate that encapsulation stress is quite different than salt stress in terms of gene expression response. Furthermore, a number of hypothetical and unknown proteins associated with encapsulation and alcohol stress have been identified, with implications for improving encapsulation protocols and rationally engineering microorganisms for direct biofuel production. 16 samples; 4 biological replicates each of 4 treatments
Project description:RNA-seq analysis of recombinant Synechocystis sp. 6803 provides important insights for understanding polyhydroxyalkanoate production in cyanobacteria under photoautotrophic conditions
Project description:The general acclimation of cyanobacteria to low carbon (LC) conditions includes coordinated alterations of gene expression and metabolism. To analyze possible signals for LC sensing and compensating reactions, we compared wild-type (WT) cells with two mutants of Synechocystis, the carboxysome-less mutant ccmM and the photorespiratory mutant ΔglcD1/D2. Metabolic phenotyping revealed that the mutant ΔccmM accumulated high 2-phosphoglycolate (2PG) levels while the ΔglcD1/D2 mutant accumulated glycolate, indicating oxygenase activity of RubisCO at high carbon (HC). The changes in the metabolite spectrum were compared to alterations in the global gene expression pattern. Cells of HC-grown mutants ΔccmM and ΔglcD1/D2 showed altered mRNA levels for many genes involved in photosynthesis, high light stress, and N-assimilation, while LC-specific genes such as those for inorganic carbon (Ci) transporters were not increased. After a shift to LC, mutant ΔglcD1/D2 revealed gene expression changes similar to WT cells, while mutant ΔccmM showed no differential expression of most LC-induced genes under identical conditions. In fact, none of the genes for Ci transporters or other components of the carbon concentrating mechanism (CCM) displayed higher transcript levels in the ΔccmM mutant. This finding renders a direct role for 2PG as a metabolic signal component for the induction of CCM during LC acclimation less likely. Because, the transcription pattern of ΔglcD1/D2 under LC showed specific differences compared to WT, a potential role for glycolate as a signal molecule that may trigger expression of parts of the CCM is proposed. Transcriptional profiling of carboxysomal and photorespiratory mutants of Synechocystis sp. PCC 6803 under high carbon (HC) and low carbon (LC) conditions relative to the wildtype response.
Project description:In eubacteria, replacement of one σ factor in the RNA polymerase (RNAP) holoenzyme by another one changes the transcription pattern. Cyanobacteria are eubacteria characterized by oxygenic photosynthesis and they typically encode numerous group 2 σ factors that closely resemble the essential primary σ factor. A mutant strain of the model cyanobacterium Synechocystis sp. PCC 6803 without functional group 2 σ factors (named as ΔsigBCDE) could not acclimate to heat, high salt, or bright light stress but in standard conditions ΔsigBCDE grew only 9% slower than the control strain. One-fifth of the genes in ΔsigBCDE were differently expressed compared to the control strain in standard growth conditions and several physiological changes in photosynthesis, and pigment and lipid compositions were detected. To directly analyze the σ factor content of RNAP holoenzyme in vivo, a His-tag was added to the γ subunit of RNAP in Synechocystis and RNAPs were collected. The results revealed that all group 2 σ factors were recruited by RNAP in standard conditions, but recruitment of SigB and SigC increased in heat stress, SigD in bright light, SigE in darkness and SigB, SigC and SigE in high salt, explaining the poor acclimation of ΔsigBCDE to these stress conditions. Cells from cyanobacteria Synechocystis sp. PCC 6803 named as control strain (CS) and a mutant strain without any functional group 2 sigma factors, ΔsigBCDE, were harvested (A730=1, 40 mL) directly from standard growth conditions (continuous illumination at the PPFD of 40 µmol m-2s-1, 32°C, ambient CO2). From three to four independent experiments were performed at each conditions.
Project description:The catalytic core of the RNA polymerase of most eubacteria is composed of two α subunits and β, β’ and ω subunits. In Escherichia coli, the ω subunit (encoded by the rpoZ gene) has been suggested to assist β’ during RNA polymerase core assembly. The function of the ω subunit is particularly interesting in cyanobacteria because the cyanobacterial β’ is split to N-terminal γ and C-terminal β’ subunits. The ∆rpoZ strain of the cyanobacterium Synechocystis sp. PCC 6803 grew well in standard conditions although the mutant cells showed low light-saturated photosynthetic activity, low Rubisco content and accumulated high quantities of protective carotenoids and α-tocopherol. The ∆rpoZ strain contained 15% less of the primary σ factor, SigA, than the control strain, and recruitment of SigA to the RNA polymerase core was inefficient in ∆rpoZ. Thus, a cyanobacterial RNA polymerase holoenzyme lacking the ω subunit contains less frequently the primary σ factor. A DNA microarray analysis revealed that this leads to specific down-regulation of highly expressed genes, like genes encoding subunits for Rubisco, ATP synthase, NADH-dehydrogenase and carbon concentrating mechanisms. On the contrary, many genes showing only low or moderate expression in the control strain were up-regulated in ∆rpoZ. A conserved -10 region was detected in promoters showing up or down-regulation in ∆rpoZ, but -35 regions of down-regulated genes completely differed from -35 regions of up-regulated genes. Cells from cyanobacteria Synechocystis sp. PCC 6803 named as control strain (CS) and RNA polymerase omega subunit inactivation strain, ΔrpoZ, were harvested (A730=1, 40 mL) directly from standard growth conditions (continuous illumination at the PPFD of 40 µmol m-2s-1, 32°C, ambient CO2). From three to four independent experiments were performed at each conditions.