Low-carbon acclimation in carboxysome-less and photorespiratory mutants of the cyanobacterium Synechocystis sp. strain PCC 6803.
ABSTRACT Using metabolic and transcriptomic phenotyping, we studied acclimation of cyanobacteria to low inorganic carbon (LC) conditions and the requirements for coordinated alteration of metabolism and gene expression. To analyse possible metabolic signals for LC sensing and compensating reactions, the carboxysome-less mutant ΔccmM and the photorespiratory mutant ΔglcD1/D2 were compared with wild-type (WT) Synechocystis. Metabolic phenotyping revealed accumulation of 2-phosphoglycolate (2PG) in ΔccmM and of glycolate in ΔglcD1/D2 in LC- but also in high inorganic carbon (HC)-grown mutant cells. The accumulation of photorespiratory metabolites provided evidence for the oxygenase activity of RubisCO at HC. The global gene expression patterns of HC-grown ΔccmM and ΔglcD1/D2 showed differential expression of many genes involved in photosynthesis, high-light stress and N assimilation. In contrast, the transcripts of LC-specific genes, such as those for inorganic carbon transporters and components of the carbon-concentrating mechanism (CCM), remained unchanged in HC cells. After a shift to LC, ΔglcD1/D2 and WT cells displayed induction of many of the LC-inducible genes, whereas ΔccmM lacked similar changes in expression. From the coincidence of the presence of 2PG in ΔccmM without CCM induction and of glycolate in ΔglcD1/D2 with CCM induction, we regard a direct role for 2PG as a metabolic signal for the induction of CCM during LC acclimation as less likely. Instead, our data suggest a potential role for glycolate as a signal molecule for enhanced expression of CCM genes.
- SourceAvailable from: Stefan Timm[Show abstract] [Hide abstract]
ABSTRACT: Being intimately intertwined with (C3) photosynthesis, photorespiration is an incredibly high flux-bearing pathway. Traditionally, the photorespiratory cycle was viewed as closed pathway to refill the Calvin–Benson cycle with organic carbon. However, given the network nature of metabolism, it hence follows that photorespiration will interact with many other pathways. In this article, we review current understanding of these interactions and attempt to define key priorities for future research, which will allow us greater fundamental comprehension of general metabolic and developmental consequences of perturbation of this crucial metabolic process.Plant Biology 09/2012; · 2.32 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: SUMMARY Cyanobacteria are the globally dominant photoautotrophic lineage. Their success is dependent on a set of adaptations collectively termed the CO2-concentrating mechanism (CCM). The purpose of the CCM is to support effective CO2 fixation by enhancing the chemical conditions in the vicinity of the primary CO2-fixing enzyme, d-ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO), to promote the carboxylase reaction and suppress the oxygenase reaction. In cyanobacteria and some proteobacteria, this is achieved by encapsulation of RubisCO within carboxysomes, which are examples of a group of proteinaceous bodies called bacterial microcompartments. Carboxysomes encapsulate the CO2-fixing enzyme within the selectively permeable protein shell and simultaneously encapsulate a carbonic anhydrase enzyme for CO2 supply from a cytoplasmic bicarbonate pool. These bodies appear to have arisen twice and undergone a process of convergent evolution. While the gross structures of all known carboxysomes are ostensibly very similar, with shared gross features such as a selectively permeable shell layer, each type of carboxysome encapsulates a phyletically distinct form of RubisCO enzyme. Furthermore, the specific proteins forming structures such as the protein shell or the inner RubisCO matrix are not identical between carboxysome types. Each type has evolutionarily distinct forms of the same proteins, as well as proteins that are entirely unrelated to one another. In light of recent developments in the study of carboxysome structure and function, we present this review to summarize the knowledge of the structure and function of both types of carboxysome. We also endeavor to cast light on differing evolutionary trajectories which may have led to the differences observed in extant carboxysomes.Microbiology and molecular biology reviews: MMBR 09/2013; 77(3):357-79. · 12.59 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Phosphoglycerate-mutase (PGM) is an ubiquitous glycolytic enzyme, which in eukaryotic cells can be found in different compartments. In prokaryotic cells, several PGMs are annotated/localized in one compartment. The identification and functional characterization of PGMs in prokaryotes is therefore important for better understanding of metabolic regulation. Here we introduce a method, based on a multi-level kinetic model of the primary carbon metabolism in cyanobacterium Synechococcus elongatus PCC 7942, that allows the identification of a specific function for a particular PGM. The strategy employs multiple parameter estimation runs in high CO2, combined with simulations testing a broad range of kinetic parameters against the changes in transcript levels of annotated PGMs. Simulations are evaluated for a match in metabolic level in low CO2, to reveal trends that can be linked to the function of a particular PGM. A one-isoenzyme scenario shows that PGM2 is a major regulator of glycolysis, while PGM1 and PGM4 make the system robust against environmental changes. Strikingly, combining two PGMs with reverse transcriptional regulation allows both features. A conclusion arising from our analysis is that a two-enzyme PGM system is required to regulate the flux between glycolysis and the Calvin-Benson cycle, while an additional PGM increases the robustness of the system.PLoS ONE 01/2013; 8(3):e58281. · 3.53 Impact Factor