Silencing and Reactivation of Urease in Yersinia pestis Is Determined by One G Residue at a Specific Position in the ureD Gene

Abstract

Yersinia pestis, the plague agent, is a naturally nonureolytic microorganism, while all other Yersinia species display a potent urease activity. In this report we demonstrate that Y. pestis harbors a complete urease locus composed of three structural (ureABC) and four accessory (ureEFGD) genes. Absence of ureolytic activity is due to the presence of one additional G residue in a poly(G) stretch, which introduces a premature stop codon in ureD. The presence of the same additional G in eight other Y. pestis isolates indicates that this mutation is species specific. Spontaneous excision of the extra G occurs at a frequency of 10 ؊4 to 10 ؊5 and restores a ureolytic phenotype to Y. pestis. The virulence of two independent ureolytic clones of Y. pestis injected either intravenously, subcutaneously, or intragastrically did not differ from that of the parental strain in the mouse infection model. Coinfection experiments with an equal number of ureolytic and nonureolytic bacteria did not evidence any difference in the ability of the two variants to multiply in vivo and to cause a lethal infection. Altogether our results demonstrate that variation of one extra G residue in ureD determines the ureolytic activity of Y. pestis but does not affect its virulence for mice or its ability to multiply and disseminate.Yersinia pestis and Yersinia pseudotuberculosis are gram-negative bacteria pathogenic for animals and humans. The former is transmitted by fleas and is responsible for plague, a fatal systemic infectious disease, whereas the latter causes a selflimiting mesenteric lymphadenitis and is transmitted by the oral route (10). Although Y. pestis and Y. pseudotuberculosis have distinct cycles of transmission and induce infection with different clinical manifestations, they are genetically closely related, with a DNA relatedness superior to 90% as determined by DNA-DNA hybridization (4). Sequence comparisons of homologous genes from both microorganisms revealed nucleotide identities ranging from 97 to 99% (1,9,28,32,33,35,36,39,40), and recent results suggest that Y. pestis is a clone of Y. pseudotuberculosis that emerged less than 20,000 years ago (1). Strikingly, several genes present in both species are intact in Y. pseudotuberculosis but mutated in Y. pestis. These include the virulence-associated plasmid (pYV)-borne gene yadA and the chromosomal invasion genes inv and ail. Nonexpression of yadA is due to a frameshift mutation in its coding sequence (33), while inactivation of inv and ail results from the disruption of their open reading frames by insertion sequences IS1541 (35) and IS285 (S. D. Torosian and R. M. Zsigray, Abstr. 96th Gen. Meet. Am. Soc. Microbiol. 1996Microbiol. , abstr. B-213, 1996, respectively. Furthermore, several phenotypic properties such as motility at 28°C; synthesis of a complete LPS molecule; and ability to ferment rhamnose and melibiose, to synthesize some amino acids (methionine, phenylalanine, threonine-glycine, and isoleucine-valine), and to degrade urea are expressed in Y. pseudotubercul...

Microarray Analysis of Temperature‐Induced Transcriptome of Yersinia pestis

“…Production of urease contributes to the pathogenicity Y. pseudotuberculosis as it is necessary for oral transmission (6). A premature stop codon introduced in the ureD gene of the ureABCEFGD operon results in the absence of ureolytic activity in Y. pestis, but does not modify the pathogenicity of Y. pestis in the mouse experimental model (30). Transcription of the whole ure operon was upregulated at 26 C (Table 3).…”

Long-term persistence of virulent Yersinia pestis in soil

“…Nowadays, in Madagascar, there are observations of pneumonic plague cases among persons attending ritual excavation of plague corpses in the absence of direct contact with the dead (Harilanto Razafindrazaka, personal communication). It has been previously suggested that Y. pestis urease may play a role in environmental adaptation (Sebbane et al, 2001). Indeed, unlike other Yersinia species, Y. pestis lacks urease activity due to a frameshift mutation (Sebbane et al, 2001).…”

Genome sequence of Yersinia pestis, the causative agent of plague

“…A similar process has been demonstrated in Y. pestis. The organism is characteristically urease negative but activity can be restored in vitro by the spontaneous deletion of a single base pair in a homopolymeric tract in ureD 22 . This type of reversible mutation would reduce the metabolic burden of producing proteins unnecessary to Y. pestis in its new¯ea/mammal life cycle yet still allow the potential to express these should a subsequent need arise.…”