Regulation of Chitin-Dependent Growth and Natural Competence in Vibrio parahaemolyticus.

Anusuya Debnath,Shin-Ichi Miyoshi,Tamaki Mizuno

doi:10.3390/microorganisms8091303

Anusuya Debnath, Shin-Ichi Miyoshi + Show 1 more

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https://doi.org/10.3390/microorganisms8091303

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Journal: Microorganisms	Publication Date: Aug 26, 2020
Citations: 13	License type: CC BY 4.0

Affiliation: Okayama University

Abstract

Vibrios can degrade chitin surfaces to soluble N-acetyl glucosamine oligosaccharides (GlcNAcn) that can be utilized as a carbon source and also induce a state of natural genetic competence. In this study, we characterized chitin-dependent growth and natural competence in Vibrio parahaemolyticus and its regulation. We found that growth on chitin was regulated through chitin sensors ChiS (sensor histidine kinase) and TfoS (transmembrane transcriptional regulator) by predominantly controlling the expression of chitinase VPA0055 (ChiA2) in a TfoX-dependent manner. The reduced growth of ΔchiA2, ΔchiS and ΔtfoS mutants highlighted the critical role played by ChiA2 in chitin breakdown. This growth defect of ΔchiA2 mutant could be recovered when chitin oligosaccharides GlcNAc2 or GlcNAc6 were supplied instead of chitin. The ΔtfoS mutant was also able to grow on GlcNAc2 but the ΔchiS mutant could not, which indicates that GlcNAc2 catabolic operon is dependent on ChiS and independent of TfoS. However, the ΔtfoS mutant was unable to utilize GlcNAc6 because the periplasmic enzymes required for the breakdown of GlcNAc6 were found to be downregulated at the mRNA level. We also showed that natural competence can be induced only by GlcNAc6, not GlcNAc2, because the expression of competence genes was significantly higher in the presence of GlcNAc6 compared to GlcNAc2. Moreover, this might be an indication that GlcNAc2 and GlcNAc6 were detected by different receptors. Therefore, we speculate that GlcNAc2-dependent activation of ChiS and GlcNAc6-dependent activation of TfoS might be crucial for the induction of natural competence in V. parahaemolyticus through the upregulation of the master competence regulator TfoX.

Highlights

Vibrio parahaemolyticus is responsible for food-borne gastroenteritis globally since isolation of the first pandemic O3:K6 strains in 1996 [1]
We found that chitinase ChiA2 plays an essential role during growth on chitin as a sole carbon source and chitin-induced natural transformation
This suggests that chitinase VPA0055 (ChiA2) played the major role in breakdown of chitin in V. parahaemolyticus

Summary

Introduction

Vibrio parahaemolyticus is responsible for food-borne gastroenteritis globally since isolation of the first pandemic O3:K6 strains in 1996 [1]. This Gram-negative, halophilic bacterium is widely disseminated in estuarine, marine and coastal surroundings either in a free-swimming state or affixed to abiotic and biotic surfaces including zooplankton, fish and shellfish [2,3]. According to the Vibrio cholerae chitin utilization pathway, it is known that the chitinase enzymes degrade chitin into GlcNAc2-6 oligosaccharides which enter either through porin or chitoporin, depending on their sizes. The binding of GlcNAc2 with CBP (chitin oligosaccharide binding protein) activates ChiS (sensor histidine kinase) which is the regulator of genes required for degradation and utilization of chitin, such as chitinases for chitin breakdown, chitoporin for transport of GlcNAcn residues into the periplasm and GlcNAc2 catabolic operon to metabolize GlcNAc2 in cytoplasm [4,8]

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