First Characterization of a Cyanobacterial Xi-Class Glutathione S-Transferase in PCC 6803.

Glutathione S-transferases (GSTs) are evolutionarily conserved enzymes crucial for cell detoxication. They are viewed as having evolved in cyanobacteria, the ancient photosynthetic prokaryotes that colonize our planet and play a crucial role for its biosphere. Xi-class GSTs, characterized by their specific glutathionyl-hydroquinone reductase activity, have been observed in prokaryotes, fungi and plants, but have not yet been studied in cyanobacteria.

Impact of Carbon Fixation, Distribution and Storage on the Production of Farnesene and Limonene in PCC 6803 and PCC 7002.

Terpenes are high-value chemicals which can be produced by engineered cyanobacteria from sustainable resources, solar energy, water and CO. We previously reported that the euryhaline unicellular cyanobacteria sp. PCC 6803 (S.

Phosphoribulokinase abundance is not limiting the Calvin-Benson-Bassham cycle in .

Improving photosynthetic efficiency in plants and microalgae is of utmost importance to support the growing world population and to enable the bioproduction of energy and chemicals. Limitations in photosynthetic light conversion efficiency can be directly attributed to kinetic bottlenecks within the Calvin-Benson-Bassham cycle (CBBC) responsible for carbon fixation. A better understanding of these bottlenecks is crucial to overcome these limiting factors through bio-engineering.

The Glutathione System: A Journey from Cyanobacteria to Higher Eukaryotes.

From bacteria to plants and humans, the glutathione system plays a pleiotropic role in cell defense against metabolic, oxidative and metal stresses. Glutathione (GSH), the γ-L-glutamyl-L-cysteinyl-glycine nucleophile tri-peptide, is the central player of this system that acts in redox homeostasis, detoxification and iron metabolism in most living organisms. GSH directly scavenges diverse reactive oxygen species (ROS), such as singlet oxygen, superoxide anion, hydrogen peroxide, hydroxyl radical, nitric oxide and carbon radicals.

Exploring the Potential of the Model Cyanobacteria PCC 7002 and PCC 7942 for the Photoproduction of High-Value Terpenes: A Comparison with PCC 6803.

We have performed the first comparative analysis of the potential of two physiologically-diverse model cyanobacteria, PCC 7002 (S.7002) and PCC 7942 (S.7942), for the photosynthetic production of four chemically-different high-value terpenes: two monoterpenes limonene and pinene, and two sesquiterpenes bisabolene and farnesene.

Biochemical and Structural Characterization of Chi-Class Glutathione Transferases: A Snapshot on the Glutathione Transferase Encoded by Gene in the Cyanobacterium sp. Strain PCC 6803.

Glutathione transferases (GSTs) constitute a widespread superfamily of enzymes notably involved in detoxification processes and/or in specialized metabolism. In the cyanobacterium sp. PCC 6803, SynGSTC1, a chi-class GST (GSTC), is thought to participate in the detoxification process of methylglyoxal, a toxic by-product of cellular metabolism.

Exploring the potential of the model cyanobacterium Synechocystis PCC 6803 for the photosynthetic production of various high-value terpenes.

Background: The robust model cyanobacterium Synechocystis PCC 6803 is increasingly explored for its potential to use solar energy, water and atmospheric CO for the carbon-neutral production of terpenes, the high-value chemicals that can be used for the production of drugs, flavors, fragrances and biofuels. However, as terpenes are chemically diverse, it is extremely difficult to predict whether Synechocystis is a suitable chassis for the photosynthetic production of various terpenes or only a few of them.

Results: We have performed the first-time engineering and comparative analysis of the best-studied cyanobacterium Synechocystis PCC 6803 for the photosynthetic production of five chemically diverse high-value terpenes: two monoterpenes (CH) limonene (cyclic molecule) and pinene (bicyclic), and three sesquiterpenes (CH) bisabolene (cyclic), farnesene (linear) and santalene (cyclic).

First analysis of the regulatory protein CP12 of the model cyanobacterium PCC 6803: Biotechnological implications.

We report the first analysis of a canonical CP12 regulatory protein, namely the unique CP12 of the model cyanobacterium PCC 6803, which has the advantage of being able to grow photoautotrophically, photomixotrophically, and photoheterotrophically. The data showed that CP12 is dispensable to cell growth under standard (continuous) light and light/dark cycle, whereas it is essential for the catabolism of exogenously added glucose that normally sustains cell growth in absence of photosynthesis. Furthermore, to be active in glucose catabolism, CP12 requires its three conserved features: its AWD_VEEL motif and its two pairs of cysteine residues.

A New Gene Family Diagnostic for Intracellular Biomineralization of Amorphous Ca Carbonates by Cyanobacteria.

Cyanobacteria have massively contributed to carbonate deposition over the geological history. They are traditionally thought to biomineralize CaCO3 extracellularly as an indirect byproduct of photosynthesis. However, the recent discovery of freshwater cyanobacteria-forming intracellular amorphous calcium carbonates (iACC) challenges this view.

Genetic, Genomics, and Responses to Stresses in Cyanobacteria: Biotechnological Implications.

Cyanobacteria are widely-diverse, environmentally crucial photosynthetic prokaryotes of great interests for basic and applied science. Work to date has focused mostly on the three non-nitrogen fixing unicellular species PCC 6803, PCC 7942, and PCC 7002, which have been selected for their genetic and physiological interests summarized in this review. Extensive "omics" data sets have been generated, and genome-scale models (GSM) have been developed for the rational engineering of these cyanobacteria for biotechnological purposes.

Methylglyoxal Detoxification Revisited: Role of Glutathione Transferase in Model Cyanobacterium sp. Strain PCC 6803.

Methylglyoxal (MG) is a detrimental metabolic by-product that threatens most organisms (in humans MG causes diabetes). MG is predominantly detoxified by the glyoxalase pathway. This process begins with the conjugation of MG with glutathione (GSH), yielding a hemithioacetal product that is subsequently transformed by the glyoxalase enzymes into d-lactate and GSH.

From Cyanobacteria to Human, MAPEG-Type Glutathione-S-Transferases Operate in Cell Tolerance to Heat, Cold, and Lipid Peroxidation.

The MAPEG2 sub-family of glutathione-S-transferase proteins (GST) has been poorly investigated , even in prokaryotes such as cyanobacteria the organisms that are regarded as having developed glutathione-dependent enzymes to protect themselves against the reactive oxygen species (ROS) often produced by their powerful photosynthesis. We report the first analysis of a cyanobacterial MAPEG2-like protein (Sll1147) in the model cyanobacterium PCC 6803. While Sll1147 is dispensable to cell growth in standard photo-autotrophic conditions, it plays an important role in the resistance to heat and cold, and to n-butyl hydroperoxide (n-BOOH) that induces lipid peroxidation.

Genomics of Urea Transport and Catabolism in Cyanobacteria: Biotechnological Implications.

Cyanobacteria are widely-diverse prokaryotes that colonize our planet. They use solar energy to assimilate huge amounts of atmospheric CO and produce a large part of the biomass and oxygen that sustain most life forms. Cyanobacteria are therefore increasingly studied for basic research objectives, as well as for the photosynthetic production of chemicals with industrial interests.

First Evidence That Glutathione-S-Transferase Operates in Photo-Oxidative Stress in Cyanobacteria.

Although glutathione (GSH) and GSH-dependent enzymes, such as glutathione transferases (GSTs), are thought to have been developed by cyanobacteria to cope with the reactive oxygen species (ROS) that they massively produced by their active photosynthesis, there had been no analysis of the role of GSTs in cyanobacteria so far. Consequently, we have analyzed two of the six GSTs of the model cyanobacterium PCC 6803, namely Sll1545 (to extend its study) and Slr0236 (because it is the best homolog to Sll1545). We report that Sll1545 is essential to cell growth in standard photo-autotrophic conditions, whereas Slr0236 is dispensable.

Overproduction of the cyanobacterial hydrogenase and selection of a mutant thriving on urea, as a possible step towards the future production of hydrogen coupled with water treatment.

Using a combination of various types of genetic manipulations (promoter replacement and gene cloning in replicating plasmid expression vector), we have overproduced the complex hydrogenase enzyme in the model cyanobacterium Synechocystis PCC6803. This new strain overproduces all twelve following proteins: HoxEFUYH (hydrogen production), HoxW (maturation of the HoxH subunit of hydrogenase) and HypABCDEF (assembly of the [NiFe] redox center of HoxHY hydrogenase). This strain when grown in the presence of a suitable quantities of nickel and iron used here exhibits a strong (25-fold) increase in hydrogenase activity, as compared to the WT strain growing in the standard medium.

Cyanobacteria: photosynthetic factories combining biodiversity, radiation resistance, and genetics to facilitate drug discovery.

Cyanobacteria are ancient, abundant, and widely diverse photosynthetic prokaryotes, which are viewed as promising cell factories for the ecologically responsible production of chemicals. Natural cyanobacteria synthesize a vast array of biologically active (secondary) metabolites with great potential for human health, while a few genetic models can be engineered for the (low level) production of biofuels. Recently, genome sequencing and mining has revealed that natural cyanobacteria have the capacity to produce many more secondary metabolites than have been characterized.

Comparative Genomics of DNA Recombination and Repair in Cyanobacteria: Biotechnological Implications.

Cyanobacteria are fascinating photosynthetic prokaryotes that are regarded as the ancestors of the plant chloroplast; the purveyors of oxygen and biomass for the food chain; and promising cell factories for an environmentally friendly production of chemicals. In colonizing most waters and soils of our planet, cyanobacteria are inevitably challenged by environmental stresses that generate DNA damages. Furthermore, many strains engineered for biotechnological purposes can use DNA recombination to stop synthesizing the biotechnological product.

Oxidative-stress detoxification and signalling in cyanobacteria: the crucial glutathione synthesis pathway supports the production of ergothioneine and ophthalmate.

Using genetics and metabolomics we investigated the synthesis (gshA and gshB genes) and catabolism (ggt) of the conserved antioxidant glutathione in the model cyanobacterium Synechocystis PCC6803. These three genes are crucial to Synechocystis, in agreement with the proposed invention of glutathione by ancient cyanobacteria to protect themselves against the toxicity of oxygen they produced through photosynthesis. Consistent with their indispensability, gshA and gshB also operate in the production of another antioxidant, ergothioneine, as well as of the glutathione analogues ophthalmate and norophthalmate.

The challenge of studying TiO2 nanoparticle bioaccumulation at environmental concentrations: crucial use of a stable isotope tracer.

The ecotoxicity of nanoparticles (NPs) is a growing area of research with many challenges ahead. To be relevant, laboratory experiments must be performed with well-controlled and environmentally realistic (i.e.

Responses to oxidative and heavy metal stresses in cyanobacteria: recent advances.

Cyanobacteria, the only known prokaryotes that perform oxygen-evolving photosynthesis, are receiving strong attention in basic and applied research. In using solar energy, water, CO2 and mineral salts to produce a large amount of biomass for the food chain, cyanobacteria constitute the first biological barrier against the entry of toxics into the food chain. In addition, cyanobacteria have the potential for the solar-driven carbon-neutral production of biofuels.

Function and Regulation of Ferredoxins in the Cyanobacterium, Synechocystis PCC6803: Recent Advances.

Ferredoxins (Fed), occurring in most organisms, are small proteins that use their iron-sulfur cluster to distribute electrons to various metabolic pathways, likely including hydrogen production. Here, we summarize the current knowledge on ferredoxins in cyanobacteria, the prokaryotes regarded as important producers of the oxygenic atmosphere and biomass for the food chain, as well as promising cell factories for biofuel production. Most studies of ferredoxins were performed in the model strain, Synechocystis PCC6803, which possesses nine highly-conserved ferredoxins encoded by monocistronic or operonic genes, some of which are localized in conserved genome regions.

Advances in the function and regulation of hydrogenase in the cyanobacterium Synechocystis PCC6803.

In order to use cyanobacteria for the biological production of hydrogen, it is important to thoroughly study the function and the regulation of the hydrogen-production machine in order to better understand its role in the global cell metabolism and identify bottlenecks limiting H2 production. Most of the recent advances in our understanding of the bidirectional [Ni-Fe] hydrogenase (Hox) came from investigations performed in the widely-used model cyanobacterium Synechocystis PCC6803 where Hox is the sole enzyme capable of combining electrons with protons to produce H2 under specific conditions. Recent findings suggested that the Hox enzyme can receive electrons from not only NAD(P)H as usually shown, but also, or even preferentially, from ferredoxin.

First proteomic study of S-glutathionylation in cyanobacteria.

Glutathionylation, the reversible post-translational formation of a mixed disulfide between a cysteine residue and glutathione (GSH), is a crucial mechanism for signal transduction and regulation of protein function. Until now this reversible redox modification was studied mainly in eukaryotic cells. Here we report a large-scale proteomic analysis of glutathionylation in a photosynthetic prokaryote, the model cyanobacterium Synechocystis sp.