ylmD and ylmE genes are dispensable for growth, cross-wall formation and sporulation in Streptomyces venezuelae .

Streptomycetes are Gram-positive filamentous soil bacteria that grow by tip extension and branching, forming a network of multinucleoid hyphae. These bacteria also have an elaborate process of morphological differentiation, which involves the formation of an aerial mycelium that eventually undergoes extensive septation into chains of uninucleoid cells that further metamorphose into spores. The tubulin-like FtsZ protein is essential for this septation process. Most of the conserved cell division genes (including ftsZ ) have been inactivated in Streptomyces without the anticipated lethality, based on studies of many other bacteria. However, there are still some genes of the Streptomyces division and cell wall ( dcw ) cluster that remain uncharacterized, the most notable example being the two conserved genes immediately adjacent to ftsZ (i.e. ylmDE ). Here, for the first time, we made a ylmDE mutant in Streptomyces venezuelae and analysed it using epifluorescence microscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The mutant showed no significant effects on growth, cross-wall formation and sporulation in comparison to the wild type strain, which suggests that the ylmDE genes do not have an essential role in the Streptomyces cell division cycle (at least under the conditions of this study).