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Photomixotrophic growth protein A (PmgA) regulates carbohydrate metabolism through the non-coding RNA Ncr0700/PmgR1 in the cyanobacterium Synechocystis sp. PCC 6803

ABSTRACT: 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.

ORGANISM(S): Synechocystis sp. PCC 6803

PROVIDER: GSE77118 | GEO | 2016/12/19

SECONDARY ACCESSION(S): PRJNA309492

REPOSITORIES: GEO

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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.

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.

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Photomixotrophic growth protein A (PmgA) regulates carbohydrate metabolism through the non-coding RNA Ncr0700/PmgR1 in the cyanobacterium Synechocystis sp. PCC 6803

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