Sigma E regulators control hemolytic activity and virulence in a shrimp pathogenic Vibrio harveyi.

TitleSigma E regulators control hemolytic activity and virulence in a shrimp pathogenic Vibrio harveyi.
Publication TypeJournal Article
Year of Publication2012
AuthorsRattanama P, Thompson JR, Kongkerd N, Srinitiwarawong K, Vuddhakul V, Mekalanos JJ
JournalPLoS One
Date Published2012
KeywordsAnimals, Bacterial Proteins, Base Sequence, Binding, Competitive, DNA Transposable Elements, Escherichia coli Proteins, Genome, Hemolysin Proteins, Hemolysis, Molecular Sequence Data, Mutagenesis, Mutation, Open Reading Frames, Penaeidae, Porins, Serine Endopeptidases, Sheep, Sigma Factor, Vibrio, Virulence

Members of the genus Vibrio are important marine and aquaculture pathogens. Hemolytic activity has been identified as a virulence factor in many pathogenic vibrios including V. cholerae, V. parahaemolyticus, V. alginolyticus, V. harveyi and V. vulnificus. We have used transposon mutagenesis to identify genes involved in the hemolytic activity of shrimp-pathogenic V. harveyi strain PSU3316. Out of 1,764 mutants screened, five mutants showed reduced hemolytic activity on sheep blood agar and exhibited virulence attenuation in shrimp (Litopenaeus vannamei). Mutants were identified by comparing transposon junction sequences to a draft of assembly of the PSU3316 genome. Surprisingly none of the disrupted open reading frames or gene neighborhoods contained genes annotated as hemolysins. The gene encoding RseB, a negative regulator of the sigma factor (σ(E)), was interrupted in 2 out of 5 transposon mutants, in addition, the transcription factor CytR, a threonine synthetase, and an efflux-associated cytoplasmic protein were also identified. Knockout mutations introduced into the rpoE operon at the rseB gene exhibited low hemolytic activity in sheep blood agar, and were 3-to 7-fold attenuated for colonization in shrimp. Comparison of whole cell extracted proteins in the rseB mutant (PSU4030) to the wild-type by 2-D gel electrophoresis revealed 6 differentially expressed proteins, including two down-regulated porins (OmpC-like and OmpN) and an upregulated protease (DegQ) which have been associated with σ(E) in other organisms. Our study is the first report linking hemolytic activity to the σ(E) regulators in pathogenic Vibrio species and suggests expression of this virulence-linked phenotype is governed by multiple regulatory pathways within the V. harveyi.

Alternate JournalPLoS ONE
PubMed ID22384269
PubMed Central IDPMC3285676