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Development of a More Sensitive and Specific Chromogenic Agar Medium for the Detection of Vibrio parahaemolyticus and Other Vibrio Species
Published on: November 8, 2016
Identification and characterization of pvuA, a gene encoding the ferric vibrioferrin receptor protein in Vibrio
Tatsuya Funahashi1, Kaoru Moriya, Sachi Uemura
1Faculty of Pharmaceutical Sciences, Okayama University, 1-1-1 Tsushima-naka, Okayama 700-8530, Japan.
Abstract:
We previously reported that Vibrio parahaemolyticus expresses two outer membrane proteins of 78 and 83 kDa concomitant with production of siderophore vibrioferrin in response to iron starvation stress and that these proteins are the ferric vibrioferrin receptor and heme receptor, respectively (S. Yamamoto, T. Akiyama, N. Okujo, S. Matsuura, and S. Shinoda, Microbiol. Immunol. 39:759-766, 1995; S. Yamamoto, Y. Hara, K. Tomochika, and S. Shinoda, FEMS Microbiol. Lett. 128:195-200, 1995). In this study, the Fur titration assay (FURTA) system was applied to isolate DNA fragments containing a potential Fur box from a genomic DNA library of V. parahaemolyticus WP1. Sequencing a 3.2-kb DNA insert in one FURTA-positive clone revealed that an amino acid sequence deduced from a partial gene, which was preceded by a full-length gene (psuA) encoding a receptor for a siderophore of unknown origin, was consistent with the N-terminal amino acid sequence of the 78-kDa ferric vibrioferrin receptor. Then, the full-length gene (pvuA) encoding the ferric vibrioferrin receptor was cloned and characterized. The deduced protein encoded by pvuA displayed the highest similarity (31% identity; 48% similarity) to RumA, a ferric rhizoferrin receptor of Morganella morganii. Primer extension and Northern blot analyses indicated that psuA and pvuA constitute an operon which is transcribed from a Fur-repressed promoter upstream of psuA. The product of the pvuA gene and its function were confirmed by generating a pvuA-disrupted mutant, coupled with genetic complementation studies. A mutant with disruption in the upstream psuA gene also displayed a phenotype impaired in the utilization of ferric vibrioferrin.
Insights
Vibrio parahaemolyticus iron uptake is regulated by the Fur protein. This study identifies the ferric vibrioferrin receptor gene (pvuA) and its operon structure, crucial for iron acquisition under starvation stress.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Physiology
Background:
- Vibrio parahaemolyticus expresses outer membrane proteins for iron acquisition during starvation.
- Previous work identified 78-kDa and 83-kDa proteins as ferric vibrioferrin and heme receptors, respectively.
Purpose of the Study:
- To identify and characterize the gene encoding the ferric vibrioferrin receptor in V. parahaemolyticus.
- To elucidate the transcriptional regulation of iron uptake genes by the Fur protein.
Main Methods:
- Fur titration assay (FURTA) for isolating DNA fragments with Fur boxes.
- Gene cloning, sequencing, and characterization of the ferric vibrioferrin receptor gene (pvuA).
- Primer extension, Northern blot analysis, gene disruption, and complementation studies.
Main Results:
- Identified and cloned the full-length gene (pvuA) for the 78-kDa ferric vibrioferrin receptor.
- Discovered that psuA and pvuA form an operon transcribed from a Fur-repressed promoter.
- Confirmed the function of the pvuA gene product through mutant analysis.
Conclusions:
- The pvuA gene encodes the ferric vibrioferrin receptor in V. parahaemolyticus.
- Iron uptake in V. parahaemolyticus is regulated by the Fur protein via repression of the psuA-pvuA operon.
- Understanding these mechanisms is vital for controlling Vibrio infections.
