Capstick David S, Willey Joanne M, Buttner Mark J, Elliot Marie A
Department of Biology, McMaster University, Hamilton, Ontario L8S4K1, Canada.
Mol Microbiol. 2007 May;64(3):602-13. doi: 10.1111/j.1365-2958.2007.05674.x.
Morphogenesis in the streptomycetes features the differentiation of substrate-associated vegetative hyphae into upwardly growing aerial filaments. This transition requires the activity of bld genes and the secretion of biosurfactants that reduce the surface tension at the colony-air interface enabling the emergence of nascent aerial hyphae. Streptomyces coelicolor produces two classes of surface-active molecules, SapB and the chaplins. While both molecules are important for aerial development, nothing is known about the functional redundancy or interaction of these surfactants apart from the observation that aerial hyphae formation can proceed via one of two pathways: a SapB-dependent pathway when cells are grown on rich medium and a SapB-independent pathway on poorly utilized carbon sources such as mannitol. We used mutant analysis to show that while the chaplins are important, but not required, for development on rich medium, they are essential for differentiation on MS (soy flour mannitol) medium, and the corresponding developmental defects could be suppressed by the presence of SapB. Furthermore, the chaplins are produced by conditional bld mutants during aerial hyphae formation when grown on the permissive medium, MS, suggesting that the previously uncharacterized SapB-independent pathway is chaplin dependent. In contrast, a bld mutant blocked in aerial morphogenesis on all media makes neither SapB nor chaplins. Finally, we show that a constructed null mutant that lacks all chaplin and SapB biosynthetic genes fails to differentiate in any growth condition. We propose that the biosurfactant activities of both SapB and the chaplins are essential for normal aerial hyphae formation on rich medium, while chaplin biosynthesis and secretion alone drives aerial morphogenesis on MS medium.
链霉菌的形态发生特征在于与底物相关的营养菌丝分化为向上生长的气生菌丝。这种转变需要bld基因的活性以及生物表面活性剂的分泌，这些生物表面活性剂可降低菌落-空气界面的表面张力，使新生气生菌丝得以出现。天蓝色链霉菌产生两类表面活性分子，即SapB和chaplins。虽然这两种分子对气生菌丝发育都很重要，但除了观察到气生菌丝形成可通过两条途径之一进行外，对于这些表面活性剂的功能冗余或相互作用一无所知：当细胞在丰富培养基上生长时为依赖SapB的途径，而在利用不佳的碳源（如甘露醇）上则为不依赖SapB的途径。我们通过突变分析表明，虽然chaplins对在丰富培养基上的发育很重要但并非必需，但它们对在MS（大豆粉甘露醇）培养基上的分化至关重要，并且相应的发育缺陷可因SapB的存在而得到抑制。此外，chaplins由条件性bld突变体在允许培养基MS上生长期间气生菌丝形成过程中产生，这表明先前未表征的不依赖SapB的途径依赖于chaplins。相反，在所有培养基上气生形态发生受阻 的bld突变体既不产生SapB也不产生chaplins。最后，我们表明构建的缺乏所有chaplin和SapB生物合成基因的无效突变体在任何生长条件下都无法分化。我们提出，SapB和chaplins的生物表面活性剂活性对于在丰富培养基上正常气生菌丝形成至关重要，而单独的chaplin生物合成和分泌驱动在MS培养基上的气生形态发生。
