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.

Inhibition of protein kinase C promotes dengue virus replication.

Background: Dengue virus (DENV) is a member of the Flaviviridae family, transmitted to human via mosquito. DENV infection is common in tropical areas and occasionally causes life-threatening symptoms. DENV contains a relatively short positive-stranded RNA genome, which encodes ten viral proteins.

IscR plays a role in oxidative stress resistance and pathogenicity of a plant pathogen, Xanthomonas campestris.

Iron-sulfur ([Fe-S]) cluster is an essential cofactor of proteins involved in various physiological processes including cellular defense against oxidative stress. In Xanthomonas campestris pv. campestris (Xcc), IscR plays a negative role in regulation of the transcription of [Fe-S] assembly genes, iscR-sufBCDS.

Engineering Synechocystis PCC6803 for hydrogen production: influence on the tolerance to oxidative and sugar stresses.

In the prospect of engineering cyanobacteria for the biological photoproduction of hydrogen, we have studied the hydrogen production machine in the model unicellular strain Synechocystis PCC6803 through gene deletion, and overexpression (constitutive or controlled by the growth temperature). We demonstrate that the hydrogenase-encoding hoxEFUYH operon is dispensable to standard photoautotrophic growth in absence of stress, and it operates in cell defense against oxidative (H₂O₂) and sugar (glucose and glycerol) stresses. Furthermore, we showed that the simultaneous over-production of the proteins HoxEFUYH and HypABCDE (assembly of hydrogenase), combined to an increase in nickel availability, led to an approximately 20-fold increase in the level of active hydrogenase.

Exopolysaccharides protect Synechocystis against the deleterious effects of titanium dioxide nanoparticles in natural and artificial waters.

We have studied the effect of TiO2 nanoparticles (NPs) on the model cyanobacteria Synechocystis PCC6803. We used well-characterized NPs suspensions in artificial and natural (Seine River, France) waters. We report that NPs trigger direct (cell killing) and indirect (cell sedimentation precluding the capture of light, which is crucial to photosynthesis) deleterious effects.

Influence of exopolysaccharides on the electrophoretic properties of the model cyanobacterium Synechocystis.

The influence of extracellular polymeric substances (EPS) on cell electrokinetics was investigated in the model cyanobacterium Synechocystis, in wild-type strains and in ten EPS-depleted mutants. The charge density and the softness of the EPS polyelectrolyte layer were calculated from the dependence of the electrophoretic mobility values of the cells with the ionic strength of the surrounding fluid. Electrophoretic mobility data showed that the eleven Synechocystis strains investigated behave as soft particles and cannot be adequately described by classical electrokinetic models of rigid particles.

Multidisciplinary evidences that Synechocystis PCC6803 exopolysaccharides operate in cell sedimentation and protection against salt and metal stresses.

Little is known about the production of exopolysaccharides (EPS) in cyanobacteria, and there are no genetic and physiological evidences that EPS are involved in cell protection against the frequently encountered environmental stresses caused by salt and metals. We studied four presumptive EPS production genes, sll0923, sll1581, slr1875 and sll5052, in the model cyanobacterium Synechocystis PCC6803, which produces copious amounts of EPS attached to cells (CPS) and released in the culture medium (RPS) as shown here. We show that sll0923, sll1581, slr1875 and sll5052 are all dispensable to the growth of all corresponding single and double deletion mutants in absence of stress.

Pseudomonas aeruginosa thiol peroxidase protects against hydrogen peroxide toxicity and displays atypical patterns of gene regulation.

The Pseudomonas aeruginosa PAO1 thiol peroxidase homolog (Tpx) belongs to a family of enzymes implicated in the removal of toxic peroxides. We have shown the expression of tpx to be highly inducible with redox cycling/superoxide generators and diamide and weakly inducible with organic hydroperoxides and hydrogen peroxide (H(2)O(2)). The PAO1 tpx pattern is unlike the patterns for other peroxide-scavenging genes in P.

Mutations of ferric uptake regulator (fur) impair iron homeostasis, growth, oxidative stress survival, and virulence of Xanthomonas campestris pv. campestris.

Iron is essential in numerous cellular functions. Intracellular iron homeostasis must be maintained for cell survival and protection against iron's toxic effects. Here, we characterize the roles of Xanthomonas campestris pv.

The catalase-peroxidase KatG is required for virulence of Xanthomonas campestris pv. campestris in a host plant by providing protection against low levels of H2O2.

Xanthomonas campestris pv. campestris katG encodes a catalase-peroxidase that has a role in protecting the bacterium against micromolar concentrations of H(2)O(2). A knockout mutation in katG that causes loss of catalase-peroxidase activity correlates with increased susceptibility to H(2)O(2) and a superoxide generator and is avirulent in a plant model system.

Mini-Tn7 vectors as genetic tools for gene cloning at a single copy number in an industrially important and phytopathogenic bacteria, Xanthomonas spp.

Transposon mini-Tn7 vectors insert into the chromosome of several Gram-negative bacteria in a site-specific manner. Here, we showed the application of mini-Tn7 as single copy site-specific integration vector system for Xanthomonas campestris pv. campestris.