Morphological Differentiation in a Filamentous Bacterium

9727234 Losick本项目的目标是阐明在丝状细菌天蓝色链霉菌中控制气生菌丝体形成过程的信号和信号通路的性质。气生菌丝体的形成取决于所谓的bld（即，“秃”）基因，其突变体产生光滑、无毛的菌落。bld突变体的一个显著特性是，当它们生长在某些其他bld突变体附近但不与它们接触时，它们能够重新获得形成气生菌丝体的能力，这种现象被称为胞外互补。将进行实验以纯化刺激气生菌丝体形成的细胞外因子。一种这样的因子通过肽导入器被转运到细胞中，并且将克隆其生产所需的基因。在传统的发育突变体的搜索中，许多bld突变体可能由于在高集落密度条件下野生型集落的胞外互补而被遗漏。现在将通过在低集落密度下进行筛选来寻找其他的bld突变体，并且将克隆和表征突变的bld基因。最后，为了便于发现更多的bld基因，将开发一种产生插入突变体的新方法。 气生菌丝体的形成是原核生物形态分化中最引人注目的例子之一。天蓝色链霉菌和其他链霉菌是丝状细菌，通过形成霉菌样的多核菌丝分支网络而生长。气生菌丝体由菌丝组成，这些菌丝远离殖民地表面生长到空气中，形成毛发状细丝的繁茂草坪，最终变形为有色孢子链。殖民地可以被认为是一种群落，其中细胞彼此活跃地交流，以协调气生菌丝体的形成。预计该项目将有助于阐明气生菌丝体形成的细胞间相互作用的性质。这项工作的发现可能会为其他种类的细菌以及高等生物细胞使用的信号系统提供见解。

9727234 Losick The goal of this project is to elucidate the nature of the signals and the signaling pathways that govem the process of aerial mycelium formation in the filamentous bacterium Streptornyces coelicolor. The formation of the aerial mycelium depends on so-called bld (i.e., "bald") genes, mutants of which produce smooth, hairless colonies. A striking property of bld mutants is their capacity to regain the ability to form an aerial mycelium when grown near, but not in contact with, certain other bld mutants, a phenomenon known as extracellular complementation. Experiments will be carried out to purify extracellular factors that stimulate the formation of the aerial mycelium. One such factor is transported into cells by a peptide importer, and a gene required for its production will be cloned. In traditional searches for developmental mutants, many bld mutants were probably missed due to extracellular complementation by wildtype colonies under conditions of high colony density. Additional bld mutants will now be sought by carrying out screens at low colony density, and the mutated bld genes will be cloned and characterized. Finally, to facilitate the discovery of additional bld genes, a new procedure for generating insertional mutants will be developed. Aerial mycelium formation is one of the most fascinating and dramatic examples of morphological differentiation in the world of procaryotic organisms. Streptomyces coelicolor and other streptomycetes are filamentous bacteria that grow by the formation of a mold-like, branching network of multinucleoid hyphae. The aerial mycelium consists of hyphae that grow into the air away from the colony surface to form a luxuriant lawn of hair-like filaments that eventually metamorphose into chains of pigmented spores. The colony can be thought of as a kind of community in which the cells are in active communication with one another so as to coordinate the formation of the aerial mycelium. It is anticipated that this project will help elucidate the nature of the intercellular interactions that govern aerial mycelium formation. It is likely that the findings derived from this work will provide insights into signaling systems used by other kinds of bacteria as well as by cells of higher organisms.