The cell division genes ftsQ and ftsZ, but not the three downstream open reading frames YFIH, ORF5 and ORF6, are essential for growth and viability in Brevibacterium lactofermentum ATCC 13869.

The three ORFs (YFIH, ORF5 and ORF6) located downstream of the cell division genes ftsQ and ftsZ in Brevibacterium lactofermentum were disrupted by single homologous recombination events between internal fragments of the corresponding genes and the chromosomal sequences. The phenotypes of the disrupted mutants were similar to that of the wild type, suggesting that these genes are dispensable for growth and viability. However, using different plasmid constructs, it was not possible to obtain disrupted ftsZ or ftsQ mutants by single crossover events. When the ftsZ or ftsQ gene sequence was disrupted in vitro and used to replace the homologous chromosomal gene by double recombination, only single recombination events took place, and therefore no disruptants were obtained. It may be concluded therefore that, as in Escherichia coli, the cell division genes ftsQ and ftsZ are indispensable for growth and viability of B. lactofermentum. Northern hybridisation analyses performed using internal fragments of the genes coding for YFIH, ORF5 and ORF6 allowed us to dissect their transcriptional organization and to confirm the disruption of these genes.