Almost all bacteria are enveloped by a cell wall that provides cellular protection. In this thesis I show that some filamentous actinomycetes have a surprising natural ability to adopt a cell wall... Show moreAlmost all bacteria are enveloped by a cell wall that provides cellular protection. In this thesis I show that some filamentous actinomycetes have a surprising natural ability to adopt a cell wall-deficient life style. The formation of these newly identified S-cells is a transient morphological adaptation in response to hyperosmotic stress conditions. In contrast, prolonged exposure to cell wall-targeting antibiotics or osmotic stress leads to the formation of so-called L-form cells, which are mutants that can proliferate indefinitely without their cell wall. The exciting properties of L-forms were used to discover a new cell-wall biosynthetic enzyme and to study enzyme secretion in the absence of a cell wall. Show less
Ramijan Carmiol, A.K.; Ultee, E.; Willemse, J.J.; Zhang, Z.; Wondergem, A.J.; Meij, A. van der; ... ; Claessen, D. 2018
The cell wall is a shape-defining structure that envelopes almost all bacteria and protects them from environmental stresses. Bacteria can be forced to grow without a cell wall under certain... Show moreThe cell wall is a shape-defining structure that envelopes almost all bacteria and protects them from environmental stresses. Bacteria can be forced to grow without a cell wall under certain conditions that interfere with cell wall synthesis, but the relevance of these wall-less cells (known as L-forms) is unclear. Here, we show that several species of filamentous actinomycetes have a natural ability to generate wall-deficient cells in response to hyperosmotic stress, which we call S-cells. This wall-deficient state is transient, as S-cells are able to switch to the normal mycelial mode of growth. However, prolonged exposure of S-cells to hyperosmotic stress yields variants that are able to proliferate indefinitely without their cell wall, similarly to L-forms. We propose that formation of wall-deficient cells in actinomycetes may serve as an adaptation to osmotic stress. Show less
Ramijan Carmiol, A.K.; Wezel, G.P. van; Claessen, D. 2017
The vast majority of antibiotics are produced by filamentous soil bacteria called actinomycetes. We report here the genome sequence of the tetracycline producer "Streptomyces viridifaciens" DSM... Show moreThe vast majority of antibiotics are produced by filamentous soil bacteria called actinomycetes. We report here the genome sequence of the tetracycline producer "Streptomyces viridifaciens" DSM 40239. Given that this species has the hallmark signatures characteristic of the Kitasatospora genus, we previously proposed to rename this organism Kitasatospora viridifaciens. Show less
