Synchronous termination of replication of the two chromosomes is an evolutionary selected feature in Vibrionaceae

Abstract

Vibrio cholerae, the causative agent of the cholera disease, is commonly used as a model organism for the study of bacteria with multipartite genomes. Its two chromosomes of different sizes initiate their DNA replication at distinct time points in the cell cycle and terminate in synchrony. In this study, the time-delayed start of Chr2 was verified in a synchronized cell population. This replication pattern suggests two possible regulation mechanisms for other Vibrio species with different sized secondary chromosomes: Either all Chr2 start DNA replication with a fixed delay after Chr1 initiation, or the timepoint at which Chr2 initiates varies such that termination of chromosomal replication occurs in synchrony. We investigated these two models and revealed that the two chromosomes of various Vibrionaceae species terminate in synchrony while Chr2-initiation timing relative to Chr1 is variable. Moreover, the sequence and function of the Chr2-triggering crtS site recently discovered in V. cholerae were found to be conserved, explaining the observed timing mechanism. Our results suggest that it is beneficial for bacterial cells with multiple chromosomes to synchronize their replication termination, potentially to optimize chromosome related processes as dimer resolution or segregation.

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

“…In a previous study, we have used SHX‐based induction of stringent response to synchronize V. cholerae populations with respect to DNA replication (Kemter et al , ). We had found that V. cholerae cells contain fully replicated chromosomes after prolonged SHX treatment similar to what was observed for E. coli (Ferullo and Lovett, ).…”

“…The position of the crtS downstream of ori1 causes both chromosomes to terminate DNA replication at approximately the same time. This termination synchrony is conserved among the Vibrionaceae (Kemter et al , ). In order to reach cell doubling times shorter than the DNA replication phase during fast growth, V. cholerae can grow with overlapping DNA replication cycles, and therefore, initiate DNA replication before the ongoing round of DNA replication is finished (Stokke et al , ).…”

“…While 90% of all bacteria encode their genetic information on a single chromosome V. cholerae contains two chromosomes (Jha et al , ). Genomes of some commonly studied O1 El Tor strains, such as N16961 or A1552 consist of a larger chromosome of 3 Mbp (Chr1) and a smaller chromosome of 1 Mbp (Chr2) (Heidelberg et al , ; Allue‐Guardia et al , ; Kemter et al , ). The initiation of DNA replication of each chromosome is regulated differently (Egan and Waldor, ; Duigou et al , ).…”

A Requirement for Global Transcription Factor Lrp in Licensing Replication of Vibrio cholerae Chromosome 2

“… The 5′ but not the 3′ end of crtS is critical for its function. (A) The 153 bp crtS sequence from V. cholerae overlaid with a WebLogo ( Crooks et al, 2004 ), generated from different Vibrio species showing varied conservation along the length of the sequence, as in Kemter et al (2018) . Gray highlighted sequence denotes the minimal 70-bp that retain copy-number enhancement function of crtS in E. coli.…”

“…The structure and function of crtS are fairly well conserved in the Vibrionaceae family ( Kemter et al, 2018 ). The size of crtS (∼153-bp) is rather large for a protein binding site and is much larger than the RctB binding sites in the Chr2 replication origin (12-mers and 39-mers).…”