A Novel Pathogenicity Island Integrated Adjacent to the thrW tRNA Gene of Avian Pathogenic Escherichia coli Encodes a Vacuolating Autotransporter Toxin

Abstract

We report the complete nucleotide sequence and genetic organization of the Vat-encoding pathogenicity island (PAI) of avian pathogenic Escherichia coli strain Ec222. The 22,139-bp PAI is situated adjacent to the 3 terminus of the thrW tRNA gene, has a G؉C content of 41.2%, and includes a bacteriophage SfII integrase gene, mobile genetic elements, two open reading frames with products exhibiting sequence similarity to known proteins, and several other open reading frames of unknown function. The PAI encodes an autotransporter protein, Vat (vacuolating autotransporter toxin), which induces the formation of intracellular vacuoles resulting in cytotoxic effects similar to those caused by the VacA toxin from Helicobacter pylori. The predicted 148.3-kDa protein product possesses the three domains that are typical of serine protease autotransporters of Enterobacteriaceae: an N-terminal signal sequence of 55 amino acids, a 111.8-kDa passenger domain containing a modified serine protease site (ATSGSG), and a C-terminal outer membrane translocator of 30.5 kDa. Vat has 75% protein homology with the hemagglutinin Tsh, an autotransporter of avian pathogenic E. coli. A vat deletion mutant of Ec222 showed no virulence in respiratory and cellulitis infection models of disease in broiler chickens. We conclude that the newly described PAI and Vat may be involved in the pathogenicity of avian septicemic E. coli strain Ec222 and other avian pathogenic E. coli strains.

Analysis of the 3′ ends of tRNA as the cause of insertion sites of foreign DNA in Prochlorococcus

“…According to the χ 2 test, the observed insertions are significant at P=0.01 level, which proved that tRNA gene loci are the insertion hotspots in the genome of Prochlorococcus. Our results confirm, from a statistical perspective, many earlier observations in prokaryotes (Reiter et al, 1989;Parreira and Gyles, 2003;van Aartsen, 2008). This previous work has revealed that tRNA loci are not only central components in translation, but also commonly serve as insertion sites for mobile elements in bacteria because there is an attB (bacterial attachment site) within some tRNA genes such as Arg and Pro (Reiter et al, 1989;Semsey et al, 2002), and therefore, the presence of these tRNA genes gives rise to variable genomic regions and the observed divergence of Prochlorococcus genomes.…”

ibeA, a virulence factor of avian pathogenic Escherichia coli

“…Challenge studies indicated a significant reduction of the virulence of the ibeA mutant. Based on prevalence studies and virulence attenuation of a mutant, conclusions have been drawn for several of the virulence genes identified to date for APEC strains (Blanco et al, 1997;Delicato et al, 2003;Dozois et al, 1992Dozois et al, , 2000Parreira & Gyles, 2003). It is therefore reasonable to assume that ibeA, when present, plays a role in the pathogenicity of APEC strains.…”

“…Gene inactivation studies confirmed a role in the pathogenicity of APEC for the F1 (type 1) and P fimbrial adhesins (Dozois et al, 1992(Dozois et al, , 1996La Ragione et al, 2000a, b;Marc et al, 1998;Pourbakhsh et al, 1997), for the K1-antigen mediating resistance to phagocytosis (Mellata et al, 2003a), for the aerobactin high-affinity iron transport system (Lafont et al, 1987) and for the temperature-sensitive haemagglutinin Tsh (Dozois et al, 2000;Provence & Curtiss, 1994). Recently, Parreira & Gyles (2003) showed that a vacuolating toxin, Vat, was involved in the virulence of an APEC isolate. Another gene whose precise function remains to be elucidated is the iss gene (Binns et al, 1979); this gene is presumed to play a role in serum resistance but, if so, its role seems to be minor (Mellata et al, 2003a).…”

Serogroups and virulence genes of Escherichia coli isolated from psittacine birds

“…There are only a few reports demonstrating that E. coli strains isolated from avian can produce toxins (Tsuji et al 1990, Blanco et al 1997a, Parreira et al 1998, Salvatori et al 2001, Parreira & Gyles, 2003. None of the isolates analyzed here possessed the genes that encoded toxins LT, STa, STb, Stx1, Stx2, Hly or CNF.…”