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Category: Bacterial Pathogenesis; Microbial Genetics and Molecular Biology
Virulence-Linked Bacteriophages of Pathogenic Vibrios, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555816506/9781555813079_Chap09-1.gif /docserver/preview/fulltext/10.1128/9781555816506/9781555813079_Chap09-2.gifAbstract:
This chapter focuses on the bacteriophages of pathogenic vibrios, particularly those that have been found to contribute directly to bacterial virulence. These phages primarily target Vibrio cholerae; however, a virulence-associated phage found in V. parahaemolyticus is also discussed briefly. V. cholerae O139 appears to have evolved from an O1 El Tor strain that acquired a new cassette of genes for O antigen production. Whether the emergence of O139 as a widespread etiologic agent of cholera marks the beginning of a new, eighth cholera pandemic is being debated. The 5’ end of the prophage (-2.4 kb) is known as the RS region. It encodes proteins needed for phage gene regulation (RstR), phage replication (RstA), and phage DNA integration (RstB). Genetic studies indicate that at least two protein complexes are used by CTXφ to infect V. cholerae. Toxin-coregulated pilus (TCP), a homopolymer of TcpA, is thought to be CTXφ’s primary receptor. A hybrid Fd phage that displays the N-terminal and central domains of pIIICTX on its surface was able to infect V. cholerae, suggesting that pIIICTX is the only CTXφ protein that is needed for normal recognition and infection of its host. Studies of the lysogenic filamentous phage have yielded knowledge of new types of virus-host interactions. The authors anticipate that future studies of CTXφ will provide additional examples of how a virus and its host can coevolve in a symbiotic fashion. Furthermore, it seems likely that future studies of other pathogenic vibrios will uncover new bacteriophages that influence pathogenicity.
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(Top) Schematic diagram of the CTXϕ genome, drawn roughly to scale.Arrows show genes and the direction of transcription. Bent arrows represent the rstR, rstA, and ctxAB promoters. Solid triangles represent the 15-bp repeats found at each end of the prophage. Protein functions are indicated underneath the genes.The overall organization of the CTXϕ genome is similar to those of other filamentous phages from Vibrio species and of filamentous phages from E. coli. (Middle) Graph of the G+C content of the CTXϕ genome, calculated by use of a 100-bp sliding window.The G+C contents of ctxAB and rstR differ the most dramatically from the average %G+C.The G+C contents of rstR and the rstA promoter were calculated for rstR ET. (Bottom) Schematic diagram of RS1, a satellite phage related to CTXϕ.
(Top) Schematic diagram of the CTXϕ genome, drawn roughly to scale.Arrows show genes and the direction of transcription. Bent arrows represent the rstR, rstA, and ctxAB promoters. Solid triangles represent the 15-bp repeats found at each end of the prophage. Protein functions are indicated underneath the genes.The overall organization of the CTXϕ genome is similar to those of other filamentous phages from Vibrio species and of filamentous phages from E. coli. (Middle) Graph of the G+C content of the CTXϕ genome, calculated by use of a 100-bp sliding window.The G+C contents of ctxAB and rstR differ the most dramatically from the average %G+C.The G+C contents of rstR and the rstA promoter were calculated for rstR ET. (Bottom) Schematic diagram of RS1, a satellite phage related to CTXϕ.
Schematic representation of CTXϕ integration.The chromosomal integration site (attB) recombines with the integration site in pCTX (attP) through short regions of homology (white rectangles; equivalent to the solid triangles seen in Fig. 1 ).This process yields a single integrated prophage.
Schematic representation of CTXϕ integration.The chromosomal integration site (attB) recombines with the integration site in pCTX (attP) through short regions of homology (white rectangles; equivalent to the solid triangles seen in Fig. 1 ).This process yields a single integrated prophage.
Arrangement of CTX prophage and RS1 DNA integrated in a variety of clinical isolates of V. cholerae. Most O1 El Tor biotype strains and O139 strains (all of those shown here) have CTXϕ DNA integrated into the large chromosome (chrI). Phage DNA is typically part of an array of tandemly integrated elements.We have found that V. cholerae strain N16961 has two copies of RS1 that flank a prophage rather than a single RS1 element downstream of the prophage, as was reported previously ( 40 ). O1 classical biotype strains have CTXϕ DNA integrated into both chromosomes. Each chromosome has either a single prophage or an array of two truncated, fused prophages.
Arrangement of CTX prophage and RS1 DNA integrated in a variety of clinical isolates of V. cholerae. Most O1 El Tor biotype strains and O139 strains (all of those shown here) have CTXϕ DNA integrated into the large chromosome (chrI). Phage DNA is typically part of an array of tandemly integrated elements.We have found that V. cholerae strain N16961 has two copies of RS1 that flank a prophage rather than a single RS1 element downstream of the prophage, as was reported previously ( 40 ). O1 classical biotype strains have CTXϕ DNA integrated into both chromosomes. Each chromosome has either a single prophage or an array of two truncated, fused prophages.
Production of extrachromosomal CTXϕ DNA from a prophage array relies on a replicative process mediated by RstA. Phage DNA excision does not occur. Replication initiates at the origin of replication, which lies near the 3′ end of rstR. As the replication complex moves along the phage DNA template, it displaces a single strand of the phage genome and replaces it with a newly synthesized strand. Replication continues past the end of the prophage, into the adjacent element downstream (in this case, RS1). Replication terminates at the origin of replication of the downstream element. A single-stranded hybrid phage genome, containing DNA from both the upstream and downstream elements in the array, is then released.
Production of extrachromosomal CTXϕ DNA from a prophage array relies on a replicative process mediated by RstA. Phage DNA excision does not occur. Replication initiates at the origin of replication, which lies near the 3′ end of rstR. As the replication complex moves along the phage DNA template, it displaces a single strand of the phage genome and replaces it with a newly synthesized strand. Replication continues past the end of the prophage, into the adjacent element downstream (in this case, RS1). Replication terminates at the origin of replication of the downstream element. A single-stranded hybrid phage genome, containing DNA from both the upstream and downstream elements in the array, is then released.