Abstract
Accurate chromosome segregation to progeny cells is a fundamental process ensuring proper inheritance of genetic material. In bacteria with simple cell cycle, chromosome segregation follows replication initiation since duplicated oriC domains start segregating to opposite halves of the cell soon after they are made. ParA and ParB proteins together with specific DNA sequences are parts of the segregation machinery. ParA and ParB proteins in Pseudomonas aeruginosa are important for optimal growth, nucleoid segregation, cell division and motility. Comparative transcriptome analysis of parA null and parB null mutants versus parental P. aeruginosa PAO1161 strain demonstrated global changes in gene expression pattern in logarithmically growing planktonic cultures. The set of genes similarly affected in both mutant strains is designated Par regulon and comprises 536 genes. The Par regulon includes genes controlled by two sigma factors (RpoN and PvdS) as well as known and putative transcriptional regulators. In the absence of Par proteins, a large number of genes from RpoS regulon is induced, reflecting the need for slowing down the cell growth rate and decelerating the metabolic processes. Changes in the expression profiles of genes involved in c-di-GMP turnover point out the role of this effector in such signal transmission. Microarray data for chosen genes were confirmed by RT-qPCR analysis. The promoter regions of selected genes were cloned upstream of the promoter-less lacZ gene and analyzed in the heterologous host E. coliΔlac. Regulation by ParA and ParB of P. aeruginosa was confirmed for some of the tested promoters. Our data demonstrate that ParA and ParB besides their role in accurate chromosome segregation may act as modulators of genes expression. Directly or indirectly, Par proteins are part of the wider regulatory network in P. aeruginosa linking the process of chromosome segregation with the cell growth, division and motility.
Highlights
In eukaryotic cells a defined mitotic apparatus is involved in active segregation of chromosomes to progeny cells during cell division
Previous analysis of PAO1161 parAnull and parBnull mutants suggested that ParA and ParB proteins are involved in chromosome segregation in P. aeruginosa cells, but may play a broader role connecting chromosome partitioning with chromosome condensation, replication, cell division, regulation of gene expression and controlling different cellular processes in bacteria, e.g. motility and cell-to-cell communication [16,18]
Quality analysis of three biological replicates of studied samples from parAnull, parBnull and WT strains was done by principal component analysis (PCA) of absolute gene expression
Summary
In eukaryotic cells a defined mitotic apparatus is involved in active segregation of chromosomes to progeny cells during cell division. Studies on numerous low-copy-number plasmids revealed the existence of bacterial counterpart of a mitotic apparatus participating in active partitioning of plasmid molecules to progeny cells, and thereby in their stable maintenance in bacteria [1]. An active plasmid partitioning system consists of two proteins (so called A- and B-type) and an essential cis-acting DNA sequence, designated, by analogy to eukaryotic mitotic apparatus, the centromere-like sequence (parS or parC). The B-type proteins recognize and bind to a specific centromere-like sequence, forming the nucleoprotein complex - segrosome [2]. The A-type proteins are NTPases and provide the dynamic scaffold for segrosome movements. Direct interactions between A and B partners induce the hydrolysis of NTP, which in turn delivers energy for relocation of segrosomes [3,4]
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