Abstract
Most bacteria replicate and segregate their DNA concomitantly while growing, before cell division takes place. How bacteria synchronize these different cell cycle events to ensure faithful chromosome inheritance is poorly understood. Here, we identified a conserved and essential protein in pneumococci and related Firmicutes named CcrZ (for Cell Cycle Regulator protein interacting with FtsZ) that couples cell division with DNA replication by controlling the activity of the master initiator of DNA replication, DnaA. The absence of CcrZ causes mis-timed and reduced initiation of DNA replication, which subsequently results in aberrant cell division. We show that CcrZ from Streptococcus pneumoniae directly interacts with the cytoskeleton protein FtsZ to place it in the middle of the newborn cell where the DnaA-bound origin is positioned. Together, this work uncovers a new mechanism for the control of the bacterial cell cycle in which CcrZ controls DnaA activity to ensure that the chromosome is replicated at the right time during the cell cycle.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
We now provide several new lines of evidence that show that CcrZ controls DNA replication via a mechanism distinct of YabA. Importantly, we established a new genome-wide genetic interaction screening assay based on CRISPR interference (CRISPRi) and parallel next generation sequencing (CRISPRi-seq). Using this new approach, which is generally applicable, we identified genes to be synthetic lethal with depletion of CcrZ (FtsK and RocS). This screen also showed that YabA has a positive genetic interaction with CcrZ, in line with our suppressor mutant analysis. In addition to this exciting new system that provides further support for our model of the mode of action of CcrZ, we now show that CcrZ also has a phenotype in Bacillus subtilis. Finally, new experiments show that the midcell localization of CcrZ is crucial for its activity.
