Loss of topological relationships in a Pleurocapsalean cyanobacterium (Chroococcidiopsis sp.) with partially inactivated ftsZ

When inactivation of the cell division gene ftsZ was attempted in the Pleurocapsalean cyanobacterium Chroococcidiopsis CCMEE 029 via homologous recombination by using a both-ends truncated ftsZ fragment cloned into the suicide mobilizable plasmid pRL271, the scored transconjugants invariably died upon restreaking. The integration of plasmid pRL271-FZ into the transconjugants genome by single crossover events, leading to the generation of two mutated copies of ftsZ, characterized by whole plasmid in-between, was assessed by colony PCR. Heteroplasmic ftsZ mutants occurred mostly as cell aggregations, lacking the regularity of successive division planes. Their aberrant topology was resolved by electron transmission microscopy as resulting from the irregular clustering of distinct aggregates. These results suggested that FtsZ is essential in this cyanobacterium able of binary and multiple division and that its partial inactivation results in an impaired coordination in time and space of successive divisions undertaken by single cells.