Tillotson R D, Wösten H A, Richter M, Willey J M
Department of Biology, Hofstra University, Hempstead, NY 11549, USA.
Mol Microbiol. 1998 Nov;30(3):595-602. doi: 10.1046/j.1365-2958.1998.01093.x.
The filamentous bacterium Streptomyces coelicolor undergoes a complex process of morphological differentiation involving the formation of a dense lawn of aerial hyphae that grow away from the colony surface into the air to form an aerial mycelium. Bald mutants of S. coelicolor, which are blocked in aerial mycelium formation, regain the capacity to erect aerial structures when exposed to a small hydrophobic protein called SapB, whose synthesis is temporally and spatially correlated with morphological differentiation. We now report that SapB is a surfactant that is capable of reducing the surface tension of water from 72 mJ m-2 to 30 mJ m-2 at a concentration of 50 microgram ml-1. We also report that SapB, like the surface-active peptide streptofactin produced by the species S. tendae, was capable of restoring the capacity of bald mutants of S. tendae to erect aerial structures. Strikingly, a member (SC3) of the hydrophobin family of fungal proteins involved in the erection of aerial hyphae in the filamentous fungus Schizophyllum commune was also capable of restoring the capacity of S. coelicolor and S. tendae bald mutants to erect aerial structures. SC3 is unrelated in structure to SapB and streptofactin but, like the streptomycetes proteins, the fungal protein is a surface active agent. Scanning electron microscopy revealed that aerial structures produced in response to both the bacterial or the fungal proteins were undifferentiated vegetative hyphae that had grown away from the colony surface but had not commenced the process of spore formation. We conclude that the production of SapB and streptofactin at the start of morphological differentiation contributes to the erection of aerial hyphae by decreasing the surface tension at the colony surface but that subsequent morphogenesis requires additional developmentally regulated events under the control of bald genes.
天蓝色链霉菌这种丝状细菌会经历一个复杂的形态分化过程，其中包括形成一层致密的气生菌丝菌苔，这些气生菌丝从菌落表面向空气中生长，形成气生菌丝体。天蓝色链霉菌的光秃突变体在气生菌丝体形成过程中受阻，当暴露于一种名为SapB的小疏水蛋白时，它们会恢复形成气生结构的能力，SapB的合成在时间和空间上与形态分化相关。我们现在报告，SapB是一种表面活性剂，在浓度为50微克/毫升时能够将水的表面张力从72毫焦/平方米降低到30毫焦/平方米。我们还报告，SapB与由柔膜链霉菌产生的表面活性肽链霉菌素一样，能够恢复柔膜链霉菌光秃突变体形成气生结构的能力。令人惊讶的是，参与丝状真菌裂褶菌气生菌丝形成的疏水蛋白家族的一个成员（SC3）也能够恢复天蓝色链霉菌和柔膜链霉菌光秃突变体形成气生结构的能力。SC3在结构上与SapB和链霉菌素无关，但与链霉菌蛋白一样，这种真菌蛋白是一种表面活性剂。扫描电子显微镜显示，对细菌或真菌蛋白作出反应而产生的气生结构是未分化的营养菌丝，它们从菌落表面生长出来，但尚未开始孢子形成过程。我们得出结论，在形态分化开始时产生SapB和链霉菌素通过降低菌落表面的表面张力有助于气生菌丝的形成，但随后的形态发生需要在光秃基因控制下的其他发育调控事件。
