Functionality of Two Origins of Replication in Vibrio cholerae Strains With a Single Chromosome

Abstract

Chromosomal inheritance in bacteria usually entails bidirectional replication of a single chromosome from a single origin into two copies and subsequent partitioning of one copy each into daughter cells upon cell division. However, the human pathogen Vibrio cholerae and other Vibrionaceae harbor two chromosomes, a large Chr1 and a small Chr2. Chr1 and Chr2 have different origins, an oriC-type origin and a P1 plasmid-type origin, respectively, driving the replication of respective chromosomes. Recently, we described naturally occurring exceptions to the two-chromosome rule of Vibrionaceae: i.e., Chr1 and Chr2 fused single chromosome V. cholerae strains, NSCV1 and NSCV2, in which both origins of replication are present. Using NSCV1 and NSCV2, here we tested whether two types of origins of replication can function simultaneously on the same chromosome or one or the other origin is silenced. We found that in NSCV1, both origins are active whereas in NSCV2 ori2 is silenced despite the fact that it is functional in an isolated context. The ori2 activity appears to be primarily determined by the copy number of the triggering site, crtS, which in turn is determined by its location with respect to ori1 and ori2 on the fused chromosome.

Replication termination without a replication fork trap

“…It was notably illustrated by the observation that the termini of the different circular chromosomes harboured by bacteria with a multipartite genome, such as Vibrio cholerae , are replicated synchronously at mid-cell 3–7 . The system allowing the synchrony of termination of the two chromosome of V. cholerae is based on the fact that the secondary chromosome (chr2) initiates replication only when crtS , a non-coding locus located 690 kb downstream of oriC1 , between VC764 and VC765 genes, on the primary chromosome (chr1) has been replicated 8–11 .…”

Molecular insights into the genome dynamics and interactions between core and acquired genomes of Vibrio cholerae

“…The genus Vibrio and other members of Vibrionaceae commonly harbor two nonhomologous circular chromosomes, Chr1 and Chr2 (34). However, a recent report indicates that V. cholerae might carry a single fused chromosome instead of two chromosomes (35). Exploration of the bipartite and single chromosome-containing genomes of clinical V. cholerae isolates identified four non-self-mobilizing genomic islands (VPI-1, VPI-2, VSP-1, VSP-2) and one self-mobilizing ICE and multiple prophages (CTXΦ, RS1Φ, TLCΦ) in most of the seventh pandemic isolates.…”

Stringent response leads to continued cell division and a temporal restart of DNA replication after initial shutdown in Vibrio cholerae

“…MFA was performed as described previously (Bruhn et al , ). In the first step, reads were mapped on the corresponding replicons using qalign from the QuasR R package.…”