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

Abstract

When inactivation of the cell division geneftsZ was attempted in the Pleurocapsalean cyanobacteriumChroococcidiopsis CCMEE 029via homologous recombination by using a both-ends truncatedftsZ 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 offtsZ, characterized by whole plasmid in-between, was assessed by colony PCR. HeteroplasmicftsZ 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.