Microarray analysis of the impact of ParB excess on gene expression in Pseudomonas aeruginosa

In Pseudomonas aeruginosa, partitioning protein ParB facilitates segregation of newly replicated chromosomes but is not essential for cell survival. Unlike in other bacteria, inactivation of parB leads to major changes of the transcriptome, suggesting that, directly or indirectly, ParB plays a role in regulation of gene expression in this organism. To identify primary targets of ParB, we analysed the impact of a slight increase in ParB amount on the transcriptome using microarrays. A several-fold increased ParB level does not cause recognizable phenotypic changes but leads to significant changes in the expression of 211 loci, including transcriptional regulators of operons involved in SOS response, virulence and adaptation. Most notably, the mRNA level of genes adjacent to high affinity ParB binding sites parS1-4 close to oriC is reduced. Our data support the role of partitioning protein ParB as a transcriptional regulator in Pseudomonas aeruginosa. Pseudomonas aeruginosa PAO1161 (leu, r-, RifR) [Bartosik et al. (2009), Microbiology 155(4), 1080-1092], a derivative of PAO1, was used in this study. Cells were grown in rich medium (L broth) at 37oC with shaking 200 rpm. Arabinose (Ara) was used to induce the expression from the araBAD promoter. RNA was isolated from PAO1161 planktonic cultures grown in L broth without Ara (WT control, 2 replicates), PAO1161 (pKGB8.0.2 araBADp) cultures grown under selection in L broth with 0.02% Ara (empty vector control, 3 replicates), PAO1161 (pKGB8.62.2 araBADp-parB) cultures grown under selection in L broth without Ara (mild ParB overproduction, 3 replicates) or with 0.02% Ara (higher ParB overproduction, 3 replicates). In the final draft of the paper plasmid names have been shortened. pKGB8.0.2 is now called pKGB8 and pKGB8.62.2 is now called pKGB9.