Premium
Complementary roles of Pseudomonas aeruginosa condensins in global chromosome organization
Author(s) -
Bhowmik Bijit Kumar,
Rybenkov Valentin V
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.594.5
Subject(s) - condensin , chromosome segregation , biology , chromosome , tetr , pseudomonas aeruginosa , genetics , premature chromosome condensation , sister chromatids , homologous recombination , microbiology and biotechnology , dna , bacteria , gene , repressor , transcription factor
Condensins play a crucial role in global chromosome maintenance and organization in all forms of life. In bacteria, condensins contribute to proper resolution and segregation of sister chromatids following replication. Atypically, Pseudomonas aeruginosa strain PAO1 expresses two condensins, the canonical SMC‐ScpAB complex and the unconventional MksBEF. These two proteins belong to two different super‐families of condensins. Here we investigated the roles of SMC‐ScpAB and MksBEF in chromosome segregation of PAO1. Pseudomonas aeruginosa condensin mutants, Δ mksB and Δ smc were constructed using homologous recombination. To visualize different loci on the chromosome, arrays of tetO operators were inserted into pre‐determined positions of P. aeruginosa chromosome and used as a binding target for TetR‐CFP chimera. TetR‐CFP was expressed from a plasmid under an IPTG inducible lacUV5 promoter. Individual chromosomal loci were then observed using fluorescence microscopy while cellular morphology was characterized using phase‐contrast microscopy PAO1 chromosome segregation initiated from a unique origin ( oriC ), progressed bidirectionally and terminated at the site‐specific recombination site dif, responsible for the resolution of daughter chromosomes. Notably, the oriC and dif sites are asymmetrically positioned on the PAO1 chromosome. As a result, the left arm is about 1.6 times longer than the right arm. Thus, segregation along the arms proceeds with unequal rates. In newly born cells, the oriC was located close to mid‐cell, whereas dif site was located close to the new pole. Following replication, oriC split into two foci, relocated to the quarter positions and remained there for the rest of cell cycle. In contrast, dif site was pulled from the pole, towards the mid‐cell and split at the very end of cell cycle. We found two macrodomains on the left arm of the chromosome. Deletion of mksB did not change the longitudinal organization of PAO1 chromosome. At the same time, the sequence of chromosome segregation remained unchanged in Δ mksB cells. However, the timing of segregation of chromosomal loci were significantly altered. Interestingly, one of the macrodomains was dispersed in Δ mksB cells. Deletion of smc had a more dramatic effect. It markedly altered segregation of oriC while most of the chromosome was disorganized Our findings indicate that both SMC and MksB contribute to the global chromosome organization in P aeruginosa . SMC and MksB has complementary but non‐overlapping roles in chromosome segregation. While SMC is required for timely segregation of oriC region, MksB ensures compactness of the chromosome. Support or Funding Information This work was supported by the award OCAST HR 14–042.