Abstract
Vibrio parahaemolyticus, the leading causative agent of seafood-associated gastroenteritis, harbors two major virulence gene loci T3SS1 and Vp-PAI (T3SS2 and tdh2). ToxR is a virulence regulator of vibrios. Cell density-dependent transcriptional pattern of toxR and its regulatory actions on T3SS1 and Vp-PAI have been previously reported, but the detailed regulatory mechanisms are still obscure. In the present work, we showed that the highest transcription level of toxR occurs at an OD600 = 0.2–0.4, which may be due to the subtle repression of ToxR and the quorum-sensing (QS) master regulator AphA. We also showed that ToxR is involved in regulating the mouse lethality, enterotoxicity, cytotoxicity, and hemolytic activity of V. parahaemolyticus. ToxR binds to the multiple promoter-proximal DNA regions within the T3SS1 locus to repress their transcription. In addition, ToxR occupies the multiple promoter-proximal DNA regions of Vp-PAI locus to activate their transcription. Thus, ToxR regulates the multiple virulence phenotypes via directly acting on the T3SS1 and Vp-PAI genes. Data presented here provide a deeper understanding of the regulatory patterns of ToxR in V. parahaemolyticus.
Highlights
Vibrio parahaemolyticus is a Gram-negative halophilic bacterium that is highly abundant in estuarine and marine environments (Thompson et al, 2004)
The results showed that the mRNA level of toxR increased considerably with the increase of cell density from an OD600 value of 0.05 to 0.2, and the highest level occurred at an OD600 value of 0.2 to 0.4, but it dramatically decreased when the OD600 value was higher than 0.4 (Figure 1)
A previous study showed that the transcriptional pattern of toxR was consistent with that of aphA, which was highly expressed at low cell density (LCD) (OD600 = 0.05–0.2) when the bacteria were grown in Difco marine broth 2216 (BD Biosciences) at 37◦C (Zhang et al, 2017)
Summary
Vibrio parahaemolyticus is a Gram-negative halophilic bacterium that is highly abundant in estuarine and marine environments (Thompson et al, 2004). It is a well-known seafood-borne human pathogen that can cause acute gastroenteritis via consumption of raw or poorly cooked, contaminated seafood (Thompson et al, 2004). Strains of the serotype O3:K6 and its genetic variants were known as the pandemic group of V. parahaemolyticus with higher levels of virulence relative to other groups (Yeung and Boor, 2004; Nair et al, 2007).
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