Effects of Osmotic Stress on Rhamnolipid Synthesis and Time-Course Production of Cell-To-Cell Signal Molecules by Pseudomonas aeruginosa

Biosynthesis of biosurfactant rhamnolipids by Pseudomonas aeruginosa depends on two hierarchical quorum sensing systems, LasRI and RhlRI, which synthesize and sense the signal molecules N-(3-oxododecanoyl)-L-homoserine lactone (3OC12-HSL) and N-butyryl-L-homoserine lactone (C4-HSL), respectively. The Pseudomonas Quinolone Signal (PQS) is a third cell-to-cell signal molecule connecting these two systems, and its precursor, 2-heptyl-4-quinolone (HHQ), also constitutes a signal. The chronology of the production of signal molecules and rhamnolipids was determined during growth in PPGAS medium. Hyperosmotic condition (0.5 M NaCl) moderately affected growth, and led to intra-cellular accumulation of compatible solutes. Production of signal molecules was delayed and their highest concentrations were 2.5 to 5 fold lower than in NaCl-free PPGAS, except for HHQ, the highest concentration of which was increased. The presence of NaCl prevented rhamnolipid synthesis. When the osmoprotectant glycine betaine was added to PPGAS/NaCl medium, it was imported by the cells without being metabolized. This did not improve growth, but reestablished the time-courses of HSL and HHQ accumulation and fully or partially restored the HSL and PQS levels. It also partially restored rhamnolipid production. Quantification of mRNAs encoding enzymes involved in HSL, PQS, and rhamnolipid biosyntheses confirmed the effect of hyperosmotic stress and glycine betaine at the gene expression level

The P323L substitution in the SARS-CoV-2 polymerase (NSP12) confers a selective advantage during infection

Background The mutational landscape of SARS-CoV-2 varies at the dominant viral genome sequence and minor genomic variant population. During the COVID-19 pandemic, an early substitution in the genome was the D614G change in the spike protein, associated with an increase in transmissibility. Genomes with D614G are accompanied by a P323L substitution in the viral polymerase (NSP12). However, P323L is not thought to be under strong selective pressure. Results Investigation of P323L/D614G substitutions in the population shows rapid emergence during the containment phase and early surge phase during the first wave. These substitutions emerge from minor genomic variants which become dominant viral genome sequence. This is investigated in vivo and in vitro using SARS-CoV-2 with P323 and D614 in the dominant genome sequence and L323 and G614 in the minor variant population. During infection, there is rapid selection of L323 into the dominant viral genome sequence but not G614. Reverse genetics is used to create two viruses (either P323 or L323) with the same genetic background. L323 shows greater abundance of viral RNA and proteins and a smaller plaque morphology than P323. Conclusions These data suggest that P323L is an important contribution in the emergence of variants with transmission advantages. Sequence analysis of viral populations suggests it may be possible to predict the emergence of a new variant based on tracking the frequency of minor variant genomes. The ability to predict an emerging variant of SARS-CoV-2 in the global landscape may aid in the evaluation of medical countermeasures and non-pharmaceutical interventions

Antibiofilm Activity of the Marine Bacterium Pseudoalteromonas sp. 3J6 Against Vibrio tapetis, the Causative Agent of Brown Ring Disease.

International audienceVibrio tapetis CECT4600 is a pathogenic Gram-negative bacterium causing the brown ring disease in the Manila clam Ruditapes philippinarum. This vibriosis is induced by bacterial attachment on the periostracal lamina, yielding a decalcification of the bivalve shell. As in many bacterial species, pathogenesis is likely related to biofilm formation. The proteinaceous exoproducts of the marine bacterium Pseudoalteromonas sp. 3J6 inhibit the formation of biofilm by most of the tested marine bacteria without affecting their planktonic growth. In the present work, we examined the sensitivity of V. tapetis to Pseudoalteromonas sp. 3J6 and its exoproducts. In V. tapetis CECT4600-GFP-Pseudoalteromonas sp. 3J6 co-cultures, the latter outcompeted V. tapetis whatever the growth mode (planktonic or biofilm), which could result from a slower growth of V. tapetis. Biofilms containing only V. tapetis were grown in vitro on a glass substratum under dynamic conditions. When the glass was coated with a culture supernatant of Pseudoalteromonas sp. 3J6 (SN3J6) prior to inoculating V. tapetis CECT4600-GFP, the bacterial attachment was about fivefold lower than in control experiment without SN3J6 and the biofilm formation was delayed by about 24 h: A full biofilm was obtained at 48 versus 24 h for the control. Moreover, a preformed V. tapetis biofilm (grown on SN3J6-free glass substratum) could be disrupted by incubating it with SN3J6. This data suggest that Pseudoalteromonas sp. 3J6 is a good candidate to set up an anti-V. tapetis strategy usable in aquaculture to grow V. tapetis-free Manila clam spats

Anti-vibrio strategy: Antibiofilm activity of a marine bacterium against Vibrio tapetis CECT4600 biofilm, the causative agent of Brown Ring Disease.

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Biofilms of the Vibrio tapetis pathogen strain CECT4600, the causative agent of Brown Ring Disease

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Characterization of biofilm formed by Vibrio tapetis CECT4600, the causative agent of Brown Ring Disease

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Bacterial interactions in a marine mudflat biofilm: a Pseudomonas bacterium produces a proteinaceous molecule inhibiting the biofilm formation of a flavobacterium strain

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Colonisation de deux interfaces par des bactéries marines issues d'un biofilm benthique transitoire et d'un biofilm composite " microorganismes / produits de corrosion " permanent.

International audienceEn environnement marin, les biofilms microbiens recouvrent la plupart des surfaces solides. Lors de la formation des biofilms, la colonisation des interfaces par les microorganismes est progressive et suit une logique taxonomique et/ou fonctionnelle des espèces. Ces biofilms représentent des systèmes multi-cellulaires au sein desquels se produisent de nombreuses interactions, de compétitions et coopérations complexes encore mal comprises et que nous souhaitons explorer. Dans le cadre de ce travail, nous nous intéressons à deux types de biofilms, un biofilm benthique prélevé sur la vasière intertidale de Brouage et un biofilm formé sur acier dans le port des Minimes de La Rochelle, impliqué dans la biocorrosion des structures métalliques. L'objectif de ce travail est d'étudier les interactions bactériennes au sein de ces biofilms. Une large gamme de bactéries hétérotrophes cultivables (160) a été isolée de ces biofilms. Leur capacité à former des biofilms a été évaluée en faisant varier les interfaces de colonisation (surfaces abiotiques en verre ou en polystyrène) et les conditions de développement des biofilms (statique ou dynamique). Dans un premier temps, nous avons testé, en conditions statiques, la capacité des bactéries à adhérer aux 2 interfaces et à se développer ensuite en biofilm. Dans un deuxième temps, les 9 souches les plus aptes à établir un biofilm sur les 2 interfaces ont été testées en conditions dynamiques (chambre à flux) sur une interface en verre. Les 4 bactéries présentant les propriétés les plus intéressantes (stabilité du biofilm, architecture 3D...) ont été sélectionnées et serviront de modèles pour l'exploration des interactions microbiennes

Marine bacteria from the French Atlantic coast displaying high forming-biofilm abilities and different biofilm 3D architectures

International audienceFew studies have reported the species composition of bacterial communities in marine biofilms formed on natural or on man-made existing structures. In particular, the roles and surface specificities of primary colonizers are largely unknown for most surface types. The aim of this study was to obtain potentially pioneering bacterial strains with high forming-biofilm abilities from two kinds of marine biofilms, collected from two different surfaces of the French Atlantic coast: an intertidal mudflat which plays a central role in aquaculture and a carbon steel structure of a harbour, where biofilms may cause important damages