Crosstalk regulation among group 2- Sigma factors in Synechocystis PCC6803

BACKGROUND: The cyanobacterium Synechocystis PCC6803 contains one group 1 (sigA) and four group 2 (sigB, sigC, sigD and sigE) sigma factors. The activity of these multiple sigma factors determines the transcriptional program of this bacterium. We wanted to study the role of the group 2 sigma factors in Synechocystis. We have therefore constructed mutants of each of the group 2 sigma factors and investigated their crosstalk. RESULTS: We used quantitative RT-PCR analysis to measure the relative abundance of the sig mRNAs in the four sigma mutants. Our data indicate that a network of mutual transcriptional regulation links the expression of the sigma genes. Accordingly, an environmental stress acting on only one of the sigma factors will indirectly modify the expression of most of the other sigma factors. This was confirmed by the transcriptional analysis of the sig mRNAs as a function of nitrogen starvation. CONCLUSION: Taken together, our observations suggest that the crosstalk regulation between all group 1 and group 2 genes could be important for the adaptation of the bacterium to different environmental and physiological conditions

Inferring the connectivity of a regulatory network from mRNA quantification in Synechocystis PCC6803

A major task of contemporary biology is to understand and predict the functioning of regulatory networks. We use expression data to deduce the regulation network connecting the sigma factors of Synechocystis PCC6803, the most global regulators in bacteria. Synechocystis contains one group 1 (SigA) and four group 2 (SigB, SigC, SigD and SigE) sigma factors. From the relative abundance of the sig mRNA measured in the wild-type and the four group 2 sigma mutants, we derive a network of the influences of each sigma factor on the transcription of all other sigma factors. Internal or external stimuli acting on only one of the sigma factors will thus indirectly modify the expression of most of the others. From this model, we predict the control points through which the circadian time modulates the expression of the sigma factors. Our results show that the cross regulation between the group 1 and group 2 sigma factors is very important for the adaptation of the bacterium to different environmental and physiological conditions

The Pkn22 Ser/Thr kinase in Nostoc PCC 7120: role of FurA and NtcA regulators and transcript profiling under nitrogen starvation and oxidative stress

International audienceBackground: The filamentous cyanobacterium Nostoc sp. strain PCC 7120 can fix N2 when combined nitrogen is not available. Furthermore, it has to cope with reactive oxygen species generated as byproducts of photosynthesis and respiration. We have previously demonstrated the synthesis of Ser/Thr kinase Pkn22 as an important survival response of Nostoc to oxidative damage. In this study we wished to investigate the possible involvement of this kinase in signalling peroxide stress and nitrogen deprivation. Results: Quantitative RT-PCR experiments revealed that the pkn22 gene is induced in response to peroxide stress and to combined nitrogen starvation. Electrophoretic motility assays indicated that the pkn22 promoter is recognized by the global transcriptional regulators FurA and NtcA. Transcriptomic analysis comparing a pkn22-insertion mutant and the wild type strain indicated that this kinase regulates genes involved in important cellular functions such as photosynthesis, carbon metabolism and iron acquisition. Since metabolic changes may lead to oxidative stress, we investigated whether this is the case with nitrogen starvation. Our results rather invalidate this hypothesis thereby suggesting that the function of Pkn22 under nitrogen starvation is independent of its role in response to peroxide stress. Conclusions: Our analyses have permitted a more complete functional description of Ser/Thr kinase in Nostoc. We have decrypted the transcriptional regulation of the pkn22 gene, and analysed the whole set of genes under the control of this kinase in response to the two environmental changes often encountered by cyanobacteria in their natural habitat: oxidative stress and nitrogen deprivation

Phylum-wide comparative genomics unravel the diversity of secondary metabolism in Cyanobacteria

Peer reviewe

Highly plastic genome of Microcystis aeruginosa PCC 7806, a ubiquitous toxic freshwater cyanobacterium

Background The colonial cyanobacterium Microcystis proliferates in a wide range of freshwater ecosystems and is exposed to changing environmental factors during its life cycle. Microcystis blooms are often toxic, potentially fatal to animals and humans, and may cause environmental problems. There has been little investigation of the genomics of these cyanobacteria. Results Deciphering the 5,172,804 bp sequence of Microcystis aeruginosa PCC 7806 has revealed the high plasticity of its genome: 11.7% DNA repeats containing more than 1,000 bases, 6.8% putative transposases and 21 putative restriction enzymes. Compared to the genomes of other cyanobacterial lineages, strain PCC 7806 contains a large number of atypical genes that may have been acquired by lateral transfers. Metabolic pathways, such as fermentation and a methionine salvage pathway, have been identified, Conclusion Microcystis aeruginosa PCC 7806 appears to have adopted an evolutionary strategy relying on unusual genome plasticity to adapt to eutrophic freshwater ecosystems, a property shared by another strain of M. aeruginosa (NIES-843). Comparisons of the genomes of PCC 7806 and other cyanobacterial strains indicate that a similar strategy may have also been used by the marine strain Crocosphaera watsonii WH8501 to adapt to other ecological niches, such as oligotrophic open oceans.

Etude de la réponse au stress oxydatif chez la cyanobactérie Anabaena sp PCC 7120 (mise en évidence d'une peroxiredoxine PrxQ-A et de la cystéine défulfurase Scdb)

La photosynthèse oxygénique peut être le lieu de formation des Formes Réactives de l Oxygène (FROs). Ces espèces réactives peuvent altérer toutes les macromolécules de la cellule, générant ainsi un stress oxydatif. Les cyanobactéries étant les premiers organismes à avoir émis de l oxygène sur terre, elles ont développé très tôt au cours de l évolution des mécanismes de défense pour lutter contre le stress oxydatif. Nous nous sommes intéressés à l étude de la réponse de la cyanobactérie filamenteuse Anabaena sp. PCC 7120 à ce stress. Nous avons mis en évidence l implication d un opéron, dit pkn, dans cette réponse adaptative. Nous avons notamment caractérisé la fonction de la peroxiredoxine PrxQ-A dans la réduction des FROs de type peroxyde. Nous avons également caractérisé une protéine codée par le dernier gène de cet opéron comme étant une cystéine désulfurase. Cette classe d enzymes est impliquée dans la mobilisation du soufre dans divers processus comme la biosynthèse de la thiamine, la biosynthèse de la molybdoptérine, la thiolation des ARNt ou encore la biogénèse des centres [Fe-S]. L éventuelle relation fonctionnelle entre les différentes protéines codées par l opéron pkn et le rôle qu elles jouent dans la réponse de ce micro-organisme au stress oxydatif offrent de nouvelles perspectives à ce travail.Oxygenic photosynthesis may generate of reactive oxygen species(ROS). These reactive species can damage all the macromolecules of the cell, inducing an oxidative stress. Cyanobacteria were the first organisms producing oxygen on earth, they have developed very early in the evolution various defenses to protect themselves against deleterious effects of ROS. We are interested in studying the response of the filamentous cyanobacterium Anabaena sp. PCC7120 to oxidative stress. During this wrok, we have highlighted the involvement of an operon, the pkn operon, in this adaptive response. We have characterized the function of peroxiredoxin Prx QA in reducing peroxide. We also characterized a protein encoded by the last gene of this operon as a cysteine desulfurase. They are pyridoxal phosphate-depending enzymes involved into the mobilization of sulfur to various processes such as biosynthesis of thiamine, the biosynthesis of molybdopterin, tRNA thiolation and also the biogenesis of [Fe-S] clusters. The possible relationship between the different proteins encoded by this operon and their role in the response of Anabaena sp.PCC 7120 to oxidative stress offer interesting perspectives.AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

Stress Signaling in Cyanobacteria: A Mechanistic Overview

International audienceCyanobacteria are highly diverse, widely distributed photosynthetic bacteria inhabiting various environments ranging from deserts to the cryosphere. Throughout this range of niches, they have to cope with various stresses and kinds of deprivation which threaten their growth and viability. In order to adapt to these stresses and survive, they have developed several global adaptive responses which modulate the patterns of gene expression and the cellular functions at work. Sigma factors, two-component systems, transcriptional regulators and small regulatory RNAs acting either separately or collectively, for example, induce appropriate cyanobacterial stress responses. The aim of this review is to summarize our current knowledge about the diversity of the sensors and regulators involved in the perception and transduction of light, oxidative and thermal stresses, and nutrient starvation responses. The studies discussed here point to the fact that various stresses affecting the photosynthetic capacity are transduced by common mechanisms

Clostridial whole cell and enzyme systems for hydrogen production: current state and perspectives

International audienceStrictly anaerobic bacteria of the Clostridium genus have attracted great interest as potential cell factories for molecular hydrogen production purposes. In addition to being a useful approach to this process, dark fermentation has the advantage of using the degradation of cheap agricultural residues and industrial wastes for molecular hydrogen production. However, many improvements are still required before large-scale hydrogen production from clostridial metabolism is possible. Here we review the literature on the basic biological processes involved in clostridial hydrogen production, and present the main advances obtained so far in order to enhance the hydrogen productivity, as well as suggesting some possible future prospects

Evidence that the PatB (CnfR) factor acts as a direct transcriptional regulator to control heterocyst development and function in the cyanobacterium <i>Nostoc</i> PCC 7120

International audienceNumerous multicellular cyanobacteria are able to form specialized cells that acquire new properties to fulfill specific tasks: atmospheric nitrogen fixation for heterocysts, motility for hormogonia, and dormancy for akinetes. In addition, in the case of heterocysts, mutual interactions occur between vegetative and differentiated cells, making from these prokaryotes exciting models to investigate cell differentiation and its connection to multicellularity (Flores & Herrero, 2010). Like any differentiation, heterocyst formation follows a precise temporal dynamic in which each step is orchestrated through often interconnected transcriptional regulators. Since the early 1990s, the regulation of this process has been extensively studied in the model bacterium Nostoc (Anabaena) PCC7120 (hereafter Nostoc). When the combined nitrogen source (ammonium or nitrate) becomes limiting, this bacterium differentiates heterocyst with a semi-regular pattern along the filaments. Heterocyts are micro-oxic, non-dividing cells, that provide a suitable environmen