Deletion of theparA(soj) Homologue inPseudomonas aeruginosaCauses ParB Instability and Affects Growth Rate, Chromosome Segregation, and Motility

Abstract

The parA and parB genes of Pseudomonas aeruginosa are located approximately 8 kb anticlockwise from oriC. ParA is a cytosolic protein present at a level of around 600 molecules per cell in exponential phase, but the level drops about fivefold in stationary phase. Overproduction of full-length ParA or the N-terminal 85 amino acids severely inhibits growth of P. aeruginosa and P. putida. Both inactivation of parA and overexpression of parA in trans in P. aeruginosa also lead to accumulation of anucleate cells and changes in motility. Inactivation of parA also increases the turnover rate (degradation) of ParB. This may provide a mechanism for controlling the level of ParB in response to the growth rate and expression of the parAB operon.The ubiquitous superfamily of Walker-type ATPases is involved in many bacterial processes (7,34,45). One subfamily of these proteins, the ParA proteins, normally functions with a second protein, ParB, and in plasmid systems the combination of ParA and ParB has been associated with better-than-random segregation of low-copy-number plasmids (6,19,23). Although the plasmid partitioning systems fall into two groups on the basis of the ATPase type of component A (type I with Walker-type ATPase and type II with actin-like ATPase), the two groups seem to be unified in the general mechanism of plasmid pairing and directional separation of plasmid molecules prior to cell division. The ParB-like protein binds a centromere-like sequence and is proposed to form pairs of the plasmid molecules (12,17,30,54). The separation of replicons and their transfer towards opposite poles of the dividing cell correlate with the ability of the ParA-like protein to form a dynamic scaffold in the cells (1,3,11,41), its ATPase activity, and its ability to interact with the ParB-parS complex.Duplication of bacterial chromosomes is part of the cell cycle events leading to cell division. Data gathered during the last decade have revealed the role of many different proteins involved in replication and segregation, as well as the spatial and temporal sequence of these processes (4, 14). However, there are still many questions concerning the directional separation of chromosomes to the progeny cells and the regulation of this process. The discovery of highly conserved homologues of ParA (Walker-type ATPase) and ParB encoded by bacterial chromosomes in close vicinity to oriC (5, 18, 36, 44, 47) suggested a role for these proteins in chromosome segregation. To date, the potential roles of both the ParA and ParB proteins in cell biology have been related to regulatory cell cycle check points (8,16,37,44,48,49), positioning of oriC domains (38, 50), separation of replicated origins (37), and the translocation of the proteins to fixed cell locations (55, 61). Studies on chromosomal ParA and ParB also revealed a lack of uniformity in their action in different organisms despite the high degree of conservation at the levels of sequence and genetic organization (5,20,21,26,32,40,44,55,56,60).The aim of the work described in th...

Caulobacter requires a dedicated mechanism to initiate chromosome segregation

“…However, in most other bacteria studied, deleting ParA causes only mild segregation defects (14,15,17). A possible explanation for these differences is that when the parABS system is absent, nondedicated mechanisms of chromosome segregation take over.…”

“…Although chromosomal parABS (chr-parABS) elements are phylogenetically distinct from those found in plasmids (13), inactivating or overexpressing chr-parABS components in several species leads to elevated numbers of anucleate cells (14)(15)(16) and introduction of chr-parABS stabilizes plasmids in heterologous hosts (17)(18)(19). In vivo observations of Vibrio cholerae's chromosome I dynamics suggested a mechanism by which ParAI (chromosome I's cognate ParA) pulls on the ParBI/parSI complex to effect chromosome segregation (20).…”

Mapping of the interactions between partition proteins Delta and Omega of plasmid pSM19035 from Streptococcus pyogenes

“…Longer ParA proteins are components of type Ia plasmid partition systems and are usually involved in regulation of expression of partition genes. However, there are type Ia partition ATPases which do not contain a DNA-binding motif in the N terminus (IncC1 of RK2) or exist only in a shorter form like IncC of RA3 (IncU) (Kulinska et al, 2008) and chromosomally encoded ParA proteins (Lasocki et al, 2007;Leonard et al, 2005;Quisel & Grossman, 2000). In type Ib partition systems, ParA-like proteins are usually not transcriptional regulators and do not contain N-terminal DNA binding regions.…”

Participation of Chromosome Segregation Protein ParAI ofVibrio choleraein Chromosome Replication

“…Chromosomal Par proteins have been studied in many bacteria, including B. subtilis (35,48), Burkholderia cenocepacia (19), Caulobacter crescentus (12,21,53), Helicobacter pylori (42), Mycobacterium smegmatis (36,37), Pseudomonas aeruginosa (8,41), Pseudomonas putida (30,46), Streptomyces coelicolor (37), and Vibrio cholerae (25,64). These studies revealed several features of the par genes.…”

“…(2) Their absence or overproduction causes at least some segregation defect, indicated by increased formation of anucleate cells, abnormal nucleoid compactness, and reduced separation of origin-proximal markers. (3) They contribute to other cellular processes, which include chromosome replication, cell division, and sporulation in B. subtilis (35,54), cell division in C. crescentus and S. coelicolor (12,21,37,52), and cell motility in P. aeruginosa (41).…”