Unknown,Transcriptomics,Genomics,Proteomics

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Comparison of carboxysomal (ccmM) and photorespiratory (glcD1/D2) mutants of Synechocystis sp. PCC 6803 using metabolic and transcriptomic phenotyping

ABSTRACT: 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.

ORGANISM(S): Synechocystis sp. PCC 6803

SUBMITTER: Floyd Wittink

PROVIDER: E-GEOD-31672 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:The trophic condition related proteomes of an oxygenic photosynthetic cyanobacterium Synechocystis sp. PCC 6803 (glucose tolerant strain) were analyzed to get further insights into the metabolic traits governing the early exponential growth under photoautotrophic, mixotrophic and heterotrophic conditions. The cells were grown under constant light autotrophically (AT) in low (air-level) CO2 (ATLC) and in high CO2 (ATHC), mixotrophically (MT) in low (air-level) CO2 in the presence of glucose (MTLC) and heterotrophically in low (air-level) CO2 in the presence of glucose and only 10 min exposure to light every 24 hours (Light-Activated Heterotrophic Growth; LAHGLC). The proteomes of ATHC, MTLC and LAHGLC differed substantially from that of ATLC, particularly by downregulation of the inducible carbon concentrating mechanisms (CCM) and photorespiration related enzymes. On the contrary, under carbon-rich conditions (ATHC, MTLC, LAHGLC) the cells accumulated respiratory NAD(P)H dehydrogenase I complexes in the thylakoid membrane. In glucose supplemented cultures (MTLC, LAHGLC) a distinct NDH-2 protein, NdbA, additionally accumulated in the thylakoid membrane whilst the plasma membrane localized NdbC and ARTO decreased in abundance. The light-harvesting proteins together with the photosystem I and II subunits were uniquely depleted under LAHGLC condition, accumulated under ATHC and in MTLC remained at the level of the reference ATLC condition. The accumulation of P-transporters was unique, revealing only minor differences between ATLC and ATHC but strong up-regulation in MTLC and down-regulation in LAHGLC. This likely implies that MTLC stores energy surplus in the highly energetic bonds of polyphosphate polymer that can be used under unfavorable growth conditions. It is concluded that the rigor of cell growth in MTLC condition results to a great extent from high intracellular inorganic carbon conditions created upon glucose breakdown and release of CO2, beside the direct utilization of glucose-derived carbon skeletons for growth. This combination provides the MTLC cultures with excellent conditions for growth that often exceeds that of the mere photoautotrophic growth at high CO2.

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Comparison of carboxysomal (ccmM) and photorespiratory (glcD1/D2) mutants of Synechocystis sp. PCC 6803 using metabolic and transcriptomic phenotyping

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