ParABS Systems of the Four Replicons of<i>Burkholderia cenocepacia</i>: New Chromosome Centromeres Confer Partition Specificity

348

334

Leptospirosis is one of the most common zoonotic diseases in the world, resulting in high morbidity and mortality in humans and affecting global livestock production. Most infections are caused by either Leptospira borgpetersenii or Leptospira interrogans, bacteria that vary in their distribution in nature and rely on different modes of transmission. We report the complete genomic sequences of two strains of L. borgpetersenii serovar Hardjo that have distinct phenotypes and virulence. These two strains have nearly identical genetic content, with subtle frameshift and point mutations being a common form of genetic variation. Starkly limited regions of synteny are shared between the large chromosomes of L. borgpetersenii and L. interrogans, probably the result of frequent recombination events between insertion sequences. The L. borgpetersenii genome is Ϸ700 kb smaller and has a lower coding density than L. interrogans, indicating it is decaying through a process of insertion sequence-mediated genome reduction. Loss of gene function is not random but is centered on impairment of environmental sensing and metabolite transport and utilization. These features distinguish L. borgpetersenii from L. interrogans, a species with minimal genetic decay and that survives extended passage in aquatic environments encountering a mammalian host. We conclude that L. borgpetersenii is evolving toward dependence on a strict host-to-host transmission cycle.genome sequence ͉ leptospirosis ͉ spirochete

Section: Resultsmentioning

confidence: 59%

Genome reduction inLeptospira borgpeterseniireflects limited transmission potential

Bulach

Zuerner

Wilson

et al. 2006

348

334

“…Replacing a plasmid par locus with one from the chromosome has been shown to stabilize plasmids indicating that the chromosomal par systems can function to mediate plasmid maintenance (5,(24)(25)(26). For example, the par locus from B. subtilis containing soj (parA), spo0J (parB), and parS can be used to stabilize a miniF deleted for its par locus (sopABC) (25).…”

mentioning

confidence: 99%

Soj (ParA) DNA binding is mediated by conserved arginines and is essential for plasmid segregation

Hester

Lutkenhaus

2007

107

134

Soj is a member of the ParA family of ATPases involved in plasmid and chromosomal segregation. It binds nonspecifically and cooperatively to DNA although the function of this binding is unknown. Here, we show that mutation of conserved arginine residues that map to the surface of Bacillus subtilis Soj caused only minimal effects on nucleotide-dependent dimerization but had dramatic effects on DNA binding. Using a model plasmid partitioning system in Escherichia coli, we find that Soj DNA-binding mutants are deficient in plasmid segregation. The location of the arginines on the Soj structure explains why DNA binding depends on dimerization and was used to orient the Soj dimer on the DNA, revealing the axis of Soj polymerization. The arginine residues are conserved among other chromosomal homologues, including the ParAs from Caulobacter crescentus, Pseudomonas aeruginosa, Pseudomonas putida, Streptomyces coelicolor, and chromosome I of Vibrio cholerae indicating that DNA binding is a common feature of members of this family.

“…Several previous studies have introduced chromosomal parABS loci into an unstable derivative of the F plasmid to test their functionality in a heterologous host, Escherichia coli (11,(28)(29)(30)(31). To perform parallel experiments, we defined ParB2-binding sites (parS2).…”

mentioning

confidence: 99%

par genes and the pathology of chromosome loss in Vibrio cholerae

Yamaichi¹,

Fogel

Waldor

2007

107

The causes and consequences of chromosome loss in bacteria with multiple chromosomes are unknown. Vibrio cholerae, the causative agent of the severe diarrheal disease cholera, has two circular chromosomes. Like many other bacterial chromosomes, both V. cholerae chromosomes contain homologues of plasmid partitioning (par) genes. In plasmids, par genes act to segregate plasmid molecules to daughter cells and thereby ensure plasmid maintenance; however, the contribution of par genes to chromosome segregation is not clear. Here, we show that the chromosome II parAB2 genes are essential for the segregation of chromosome II but not chromosome I. In a parAB2 deletion mutant, chromosome II is mislocalized and frequently fails to segregate, yielding cells with only chromosome I. These cells divide once; their progeny are not viable. Instead, chromosome II-deficient cells undergo dramatic cell enlargement, nucleoid condensation and degradation, and loss of membrane integrity. The highly consistent nature of these cytologic changes suggests that prokaryotes, like eukaryotes, may possess characteristic death pathways.chromosome segregation ͉ parA ͉ parB ͉ apoptosis