Environmental Vibrio strains represent a major threat in aquaculture, but the understanding of their virulence mechanisms heavily relies on the transposition of knowledge from human-pathogen vibrios. Here, the genetic bases of the virulence of Vibrio harveyi ORM4 towards the European abalone Haliotis tuberculata were characterized. We demonstrated that luxO, encoding a major regulator of the quorum sensing system, is crucial for the virulence of this strain, and that its deletion leads to a decrease in swimming motility, biofilm formation, and exopolysaccharide production. Furthermore, the biofilm formation by V. harveyi ORM4 was increased by abalone serum, which required LuxO. The absence of LuxO in V. harveyi ORM4 yielded opposite phenotypes compared with other Vibrio species including V. campbellii (still frequently named V. harveyi). In addition, we report a full type III secretion system (T3SS) gene cluster in the V. harveyi ORM4 genome. LuxO was shown to negatively regulate the promoter activity of exsA, encoding the major regulator of the T3SS genes, and the deletion of exsA abolished the virulence of V. harveyi ORM4. These results unveil virulence mechanisms set up by this environmentally important bacterial pathogen and pave the way for a better molecular understanding of the regulation of its pathogenicity.
Volume 86, no. 20, e00893-20, 2020, https://doi.org/10.1128/AEM.00893-20. This article was published on 1 October 2020 with improper formatting for affiliation “c.” This has been corrected in the version of the article posted on 5 October 2020.
Biofilms produced by Pseudomonas aeruginosa present a serious threat to cystic fibrosis patients. Here, we report the draft genome sequences of four cystic fibrosis isolates displaying various mucoid and biofilm phenotypes. The estimated average genome size was about 6,255,986 ± 50,202 bp with a mean G+C content of 66.52 ± 0.06%.
Le biofilm est un mode de vie qui confere aux bacteries une protection contre les agents antimicrobiens et pose un probleme de sante publique qui necessite de trouver une alternative aux traitements actuels. La bacterie marine Pseudoalteromonas sp. 3J6 et ses exoproduits (SN3J6) montrent une activite antibiofilm contre des bacteries marines et terrestres. Une proteine, nommee alterocine, a ete extraite du SN3J6. Bien que presente chez plusieurs autres souches de Pseudoalteromonas, son role est encore inconnu dans les bases de donnees. Ce projet a ete consacre a l’etude de l’alterocine. Les caracteristiques de cette proteine ainsi que celles de son gene, alt, ont dans un premier temps ete etudiees. Le gene alt n’est pas organise en operon et plusieurs promoteurs potentiels ont ete identifies. Il est exprime preferentiellement durant la phase stationnaire. Il code une proteine de 139 residus incluant un peptide signal predit, qui permettrait la secretion de l’alterocine mature (119 residus). Aucune homologie de sequence n’a ete observee entre l’alterocine et les proteines de fonction connue des bases de donnees. Afin de detecter plus facilement l’alterocine dans le surnageant de culture, des anticorps anti-alterocine ont ete obtenus. Nous avons dans un second temps confirme l’activite antibiofilm de l’alterocine par une production heterologue chez une autre souche de Pseudoalteromonas et en comparant les biofilms obtenus en presence des surnageants de culture de cette souche et de sa souche mere. Nous avons montre que l’alterocine est un nouveau type de proteine antibiofilm dont la structure et le mode d’action restent a determiner pour l’utiliser comme agent antibiofilm.
We sought to identify and study the antibiofilm protein secreted by the marine bacterium Pseudoalteromonas sp. strain 3J6. The latter is active against marine and terrestrial bacteria, including Pseudomonas aeruginosa clinical strains forming different biofilm types. Several amino acid sequences were obtained from the partially purified antibiofilm protein, named alterocin. The Pseudoalteromonas sp. 3J6 genome was sequenced, and a candidate alt gene was identified by comparing the genome-encoded proteins to the sequences from purified alterocin. Expressing the alt gene in another nonactive Pseudoalteromonas sp. strain, 3J3, demonstrated that it is responsible for the antibiofilm activity. Alterocin is a 139-residue protein that includes a predicted 20-residue signal sequence, which would be cleaved off upon export by the general secretion system. No sequence homology was found between alterocin and proteins of known functions. The alt gene is not part of an operon and adjacent genes do not seem related to alterocin production, immunity, or regulation, suggesting that these functions are not fulfilled by devoted proteins. During growth in liquid medium, the alt mRNA level peaked during the stationary phase. A single promoter was experimentally identified, and several inverted repeats could be binding sites for regulators. alt genes were found in about 30% of the Pseudoalteromonas genomes and in only a few instances of other marine bacteria of the Hahella and Paraglaciecola genera. Comparative genomics yielded the hypothesis that alt gene losses occurred within the Pseudoalteromonas genus. Overall, alterocin is a novel kind of antibiofilm protein of ecological and biotechnological interest.IMPORTANCE Biofilms are microbial communities that develop on solid surfaces or interfaces and are detrimental in a number of fields, including for example food industry, aquaculture, and medicine. In the latter, antibiotics are insufficient to clear biofilm infections, leading to chronic infections such as in the case of infection by Pseudomonas aeruginosa of the lungs of cystic fibrosis patients. Antibiofilm molecules are thus urgently needed to be used in conjunction with conventional antibiotics, as well as in other fields of application, especially if they are environmentally friendly molecules. Here, we describe alterocin, a novel antibiofilm protein secreted by a marine bacterium belonging to the Pseudoalteromonas genus, and its gene. Alterocin homologs were found in about 30% of Pseudoalteromonas strains, indicating that this new family of antibiofilm proteins likely plays an important albeit nonessential function in the biology of these bacteria. This study opens up the possibility of a variety of applications.
