Design and Construction of Vibrio cholerae Strains That Harbor Various CTX Prophage Arrays.

Hyun J Yu,Eun J Kim,Da S R Cha,Dong-Hun Shin,Dong W Kim,Gopinath B Nair

doi:10.3389/fmicb.2018.00339

Hyun J Yu, Eun J Kim + Show 4 more

Open Access

https://doi.org/10.3389/fmicb.2018.00339

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Abstract

Toxigenic Vibrio cholerae strains arise upon infection and integration of the lysogenic cholera toxin phage, the CTX phage, into bacterial chromosomes. The V. cholerae serogroup O1 strains identified to date can be broadly categorized into three main groups: the classical biotype strains, which harbor CTX-cla; the prototype El Tor strains (Wave 1 strains), which harbor CTX-1; and the atypical El Tor strains, which harbor CTX-2 (Wave 2 strains) or CTX-3~6 (Wave 3 strains). The efficiencies of replication and transmission of CTX phages are similar, suggesting the possibility of existence of more diverse bacterial strains harboring various CTX phages and their arrays in nature. In this study, a set of V. cholerae strains was constructed by the chromosomal integration of CTX phages into strains that already harbored CTX phages or those that did not harbor any CTX phage or RS1 element. Strains containing repeats of the same kind of CTX phage, strains containing the same kind of CTX phage in each chromosome, strains containing alternative CTX phages in one chromosome, or containing different CTX phages in each chromosome have been constructed. Thus, strains with any CTX array can be designed and constructed. Moreover, the strains described in this study contained the toxT-139F allele, which enhances the expression of TcpA and cholera toxin. These characteristics are considered to be important for cholera vaccine development. Once their capacity to provoke immunity in human against V. cholerae infection is evaluated, some of the generated strains could be developed further to yield cholera vaccine strains.

Highlights

Vibrio cholerae is the causative agent of cholera, a severe diarrheal disease (Kaper et al, 1995; Sack et al, 2004)
The non-coding sequences of pCTX-1 and pCTX-cla differ (Kim et al, 2016). This variation directs the integration of the pCTX genome into either chromosome 1 or 2 of V. cholerae strains (Table 1; Das et al, 2010). pCTX-1, which contains the authentic noncoding sequence of CTX-1, was shown to integrate only into chromosome 1, while a plasmid that contains the non-coding sequence of CTX-cla may be integrated into the chromosome 1 and/or 2 (Das et al, 2010)
1 or 2 is determined by the attP site located within the noncoding sequence of pCTX, and the dif sequences on the bacterial chromosomes (Das et al, 2010)

Summary

Introduction

Vibrio cholerae is the causative agent of cholera, a severe diarrheal disease (Kaper et al, 1995; Sack et al, 2004). Two biotypes of V. cholerae O1 strains, the classical and El Tor biotypes, have been dominant sequentially in the history of the disease; the classical biotype strains were predominant before the 1960s, whereas the El Tor biotype strains emerged in 1961 and have globally replaced the classical biotype strains (Sack et al, 2004). Atypical El Tor strains that harbor mosaic CTX phages of CTX-1 and CTX-cla, namely CTX-2 containing the classical type rstR and ctxB or CTX-3∼CTX-6 containing the El Tor type rstR and the classical type ctxB, have been prevalent since the early 1990s (Safa et al, 2010; Kim et al, 2015)

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