Department of Biotechnology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan.
Department of Biotechnology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
J Bacteriol. 2019 Jun 21;201(14). doi: 10.1128/JB.00746-18. Print 2019 Jul 15.
The rare actinomycete produces terminal sporangia containing a few hundred flagellated spores. After release from the sporangia, the spores swim rapidly in aquatic environments as zoospores. The zoospores stop swimming and begin to germinate in niches for vegetative growth. Here, we report the characterization and functional analysis of zoospore type IV pili in The pilus gene () cluster, consisting of three apparently σ-dependent transcriptional units, is activated during sporangium formation similarly to the flagellar gene cluster, indicating that the zoospore has not only flagella but also pili. With a new method in which zoospores were fixed with glutaraldehyde to prevent pilus retraction, zoospore pili were observed relatively easily using transmission electron microscopy, showing 6 ± 3 pili per zoospore ( = 37 piliated zoospores) and a length of 0.62 ± 0.35 μm ( = 206), via observation of -deleted, nonflagellated zoospores. No pili were observed in the zoospores of a prepilin-encoding deletion (Δ) mutant. In addition, the deletion of , which encodes an ATPase predicted to be involved in pilus retraction, substantially reduced the frequency of pilus retraction. Several adhesion experiments using wild-type and Δ zoospores indicated that the zoospore pili are required for the sufficient adhesion of zoospores to hydrophobic solid surfaces. Many zoospore-forming rare actinomycetes conserve the cluster, which indicates that the zoospore pili yield an evolutionary benefit in the adhesion of zoospores to hydrophobic materials as footholds for germination in their mycelial growth. Bacterial zoospores are interesting cells in that their physiological state changes dynamically: they are dormant in sporangia, show temporary mobility after awakening, and finally stop swimming to germinate in niches for vegetative growth. However, the cellular biology of a zoospore remains largely unknown. This study describes unprecedented zoospore type IV pili in the rare actinomycete Similar to the case for the usual bacterial type IV pili, zoospore pili appeared to be retractable. Our findings that the zoospore pili have a functional role in the adhesion of zoospores to hydrophobic solid surfaces and that the zoospores use both pili and flagella properly according to their different purposes provide an important insight into the cellular biology of the zoospore.
稀有放线菌产生末端孢子囊，其中含有数百个鞭毛孢子。从孢子囊中释放出来后，孢子在水生环境中作为游动孢子迅速游动。游动孢子停止游动，并开始在营养生长的小生境中发芽。在这里，我们报告了在 中 zoospore type IV pili 的特征和功能分析。该菌的 pilus 基因（）簇由三个明显依赖于 σ 的转录单元组成，在孢子囊形成过程中与 flagellar 基因簇类似地被激活，表明游动孢子不仅有鞭毛，而且有菌毛。我们采用一种新的方法，用戊二醛固定游动孢子以防止菌毛回缩，然后通过观察 - 缺失、无鞭毛的游动孢子，相对容易地用透射电子显微镜观察到游动孢子上的菌毛，每个游动孢子有 6 ± 3 根菌毛（= 37 个带有菌毛的游动孢子），长度为 0.62 ± 0.35 μm（= 206）。在 prepilin 编码的 缺失（Δ）突变体的游动孢子中观察不到菌毛。此外，编码预测参与菌毛回缩的 ATP 酶的 的缺失，大大降低了菌毛回缩的频率。使用野生型和 Δ 游动孢子进行的几次粘附实验表明，游动孢子菌毛对于游动孢子充分粘附到疏水性固体表面是必需的。许多游动孢子形成的稀有放线菌都保守了 簇，这表明游动孢子菌毛在游动孢子粘附疏水性物质作为其菌丝体生长中发芽的立足点方面产生了进化优势。细菌游动孢子是一种有趣的细胞，因为它们的生理状态会动态变化：它们在孢子囊中休眠，在苏醒后表现出暂时的活动性，最后停止游动，在营养生长的小生境中发芽。然而，游动孢子的细胞生物学在很大程度上仍然未知。本研究描述了稀有放线菌 中前所未有的游动孢子 type IV pili。与通常的细菌 type IV pili 类似，游动孢子菌毛似乎是可回缩的。我们发现，游动孢子菌毛在游动孢子与疏水性固体表面的粘附中具有功能作用，并且游动孢子根据其不同的目的正确使用菌毛和鞭毛，这为游动孢子的细胞生物学提供了重要的见解。
