Full scale experimental campaign to determine the actual heat flux produced by fire on composite storages - calibration tests on metallic vessels

International audienceIf Hydrogen is expected to be highly valuable, some improvements should be conducted, mainly regarding the storage safety. To prevent from high pressure hydrogen composite tanks bursting, the comprehension of the thermo-mechanics phenomena in the case of fire should be improved. To understand the kinetic of strength loss, the heat flux produced by fire of various intensities should be assessed. This is the objective of this real scale experimental campaign, which will allow studying in future works, the strength loss of composite high-pressure vessels in similar fire conditions to the ones determined in this study. Fire calibration tests were performed on metallic cylinder vessels. These tests with metallic cylinders are critical in the characterization of the thermal load of various fire sources (pool fire, propane gas fire, hydrogen gas fire) so as to evaluate differences related to different thermal load. Radiant panels were also used as thermal source for reference of pure radiation heat transfer. The retained thermal load might be representative of accidental situations in worst case scenarios, and relevant for a standardized testing protocol. The tests performed show that hydrogen gas fires and heptane pool fire allow reaching the target in terms of absorbed energy, regarding the results of risk analysis performed previously. Other considerations can be taken into account that will led to retain an hydrogen gas fire for further works. Firstly, hydrogen gas fire is the more realistic scenario: Hydrogen is the combustible that we every time find near an hydrogen storage. Secondly, as one of the objectives of the project is to make recommendations for standardization issues, it’s important to note that gas fires are not too complex to calibrate, control and reproduce. Finally, due to previous considerations, Hydrogen gas fire will be retained for thermal load of composite cylinders in future works

NoeM, a new nodulation gene involved in the biosynthesis of Nod Factors with an open-chain oxidized terminal residue and in the symbiosis with Mimosa pudica

The beta-rhizobium Cupriavidus taiwanensis is a nitrogen-fixing symbiont of Mimosa pudica. Nod factors produced by this species were previously found to be pentameric chitin-oligomers carrying common C18:1 or C16:0 fatty acyl chains, N-methylated and C-6 carbamoylated on the nonreducing terminal N-acetylglucosamine and sulfated on the reducing terminal residue. Here, we report that, in addition, C. taiwanensis LMG19424 produces molecules where the reducing sugar is open and oxidized. We identified a novel nodulation gene located on the symbiotic plasmid pRalta, called noeM, which is involved in this atypical Nod factor structure. noeM encodes a transmembrane protein bearing a fatty acid hydroxylase domain. This gene is expressed during symbiosis with M. pudica and requires NodD and luteolin for optimal expression. The closest noeM homologs formed a separate phylogenetic clade containing rhizobial genes only, which are located on symbiosis plasmids downstream from a nod box. Corresponding proteins, referred to as NoeM, may have specialized in symbiosis via the connection to the nodulation pathway and the spread in rhizobia. noeM was mostly found in isolates of the Mimoseae tribe, and specifically detected in all tested strains able to nodulate M. pudica. A noeM deletion mutant of C. taiwanensis was affected for the nodulation of M. pudica, confirming the role of noeM in the symbiosis with this legume

Dynamic genomic architecture of mutualistic cooperation in a wild population of Mesorhizobium

Research on mutualism seeks to explain how cooperation can be maintained when uncooperative mutants co-occur with cooperative kin. Gains and losses of the gene modules required for cooperation punctuate symbiont phylogenies and drive lifestyle transitions between cooperative symbionts and uncooperative free-living lineages over evolutionary time. Yet whether uncooperative symbionts commonly evolve from within cooperative symbiont populations or from within distantly related lineages with antagonistic or free-living lifestyles (i.e., third-party mutualism exploiters or parasites), remains controversial. We use genomic data to show that genotypes that differ in the presence or absence of large islands of symbiosis genes are common within a single wild recombining population of Mesorhizobium symbionts isolated from host tissues and are an important source of standing heritable variation in cooperation in this population. In a focal population of Mesorhizobium , uncooperative variants that lack a symbiosis island segregate at 16% frequency in nodules, and genome size and symbiosis gene number are positively correlated with cooperation. This finding contrasts with the genomic architecture of variation in cooperation in other symbiont populations isolated from host tissues in which the islands of genes underlying cooperation are ubiquitous and variation in cooperation is primarily driven by allelic substitution and individual gene gain and loss events. Our study demonstrates that uncooperative mutants within mutualist populations can comprise a significant component of genetic variation in nature, providing biological rationale for models and experiments that seek to explain the maintenance of mutualism in the face of non-cooperators

Evolution Underway in Prokaryotes

International audienceEvolution is a phenomenon that escapes immediate attention because changes occur at a very slow pace and are often considered at odds with a religious vision of the world. Using bacteria that replicate so much faster than eukaryotes has permitted to quantify and discern tendencies. Such laboratory evolution implies growth rate, ability to use this or that substrate, but also synthesis and resistance to antibiotics and the ability to interact with eukaryotic host