Genes encoding the Vibrio harveyi haemolysin (VHH)/thermolabile haemolysin (TLH) are widespread in Vibrios

Abstract:

V. harveyi VHH haemolysin, which shows high homology to the TLH haemolysin (the identities of their deduced amino acid sequences are up to 85.6%), is a putative virulence factor to marine cultured fish. A VHH probe, which is specific to V. harveyi vhhA haemolysin gene, was used to screen EcoRⅠ digests of total DNA from 57 vibrio strains，including 26 vibrio type strains, 20 V. harveyi isolates and 11 V. parahaemolyticus isolates. As a result, 1 strong hybridisation band was detected in 13 type strains, including 2 of Vibrio alginolyticus, 2 of V. harveyi, and 1 strain each of Grimontia hollisae, V. campbellii, V. cincinnatiensis, V. fischeri, V. mimicus, V. natriegens, V. parahaemolyticus, V. proteolyticus and V. logei. Also, 1 weak band was detected in 6 type strains, including V. anguillarum, V. aestuarianus, Photobacterium damselae subsp. damselae, V. fluvialis, V. furnissii and V. vulnificus. There was not any hybridization signal in other type strains. Also, vhh/tlh was present in all isolates of V. harveyi and V. parahaemolyticus. Moreover, 3 isolates of V. harveyi，i.e. VIB 645, VIB 648 and SF1, had duplicated vhh genes. The data indicates that vhh/tlh is widespread in vibrios, especially in V. harveyi related species and V. fischeri related species. To support this conclusion, the vhh/tlh homologue genes in V. anguillarum VIB 72, V. campbellii VIB 285, V. natriegens VIB 299 and V. harveyi VIB 647 were cloned and sequenced, and the deduced amino acid sequences showed high degree of identities to VHH (67%～99%) and TLH haemolysin (69％～91%). This study will help us to identify the role of vhh/tlh haemolysin gene in the pathogenicity of vibrios.

Key words:Vibrios; V. harveyi; V. parahaemolyticus; haemolysin gene; vhh; tlh