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.
The aim was to identify and study the antibiofilm protein secreted by the marine bacterium Pseudoalteromonas sp. 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 non-active Pseudoalteromonas sp. strain, 3J3, demonstrated that it is responsible for the antibiofilm activity. Alterocin is a 139-residue protein including 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 liquid growth, 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 few instances of other marine bacteria of the Hahella and Paraglaciecola genera. Comparative genomics yielded the hypotheses 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 non-essential function in the biology of these bacteria. This work opens up the possibility of a variety of applications.
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%.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.