Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois, USA
J Bacteriol. 2019 Aug 22;201(18). doi: 10.1128/JB.00064-19. Print 2019 Sep 15.
In aquatic environments, spp. can be found at the boundary between liquid and air known as the neuston. I report an approach to study temporal features of colonization and pellicle biofilm development at the air-liquid interface and have defined the role of cell surface structures in this process. At this interface, initially forms a monolayer of cells bearing a surface adhesin known as the holdfast. When excised from the liquid surface, this monolayer strongly adheres to glass. The monolayer subsequently develops into a three-dimensional structure that is highly enriched in clusters of stalked cells known as rosettes. As this pellicle film matures, it becomes more cohesive and less adherent to a glass surface. A mutant strain lacking a flagellum does not efficiently reach the surface, and strains lacking type IV pili exhibit defects in organization of the three-dimensional pellicle. Strains unable to synthesize the holdfast fail to accumulate at the boundary between air and liquid and do not form a pellicle. Phase-contrast images support a model whereby the holdfast functions to trap cells at the air-liquid boundary. Unlike the holdfast, neither the flagellum nor type IV pili are required for to partition to the air-liquid interface. While it is well established that the holdfast enables adherence to solid surfaces, this study provides evidence that the holdfast has physicochemical properties that allow partitioning of nonmotile mother cells to the air-liquid interface and facilitate colonization of this microenvironment. In aquatic environments, the boundary at the air interface is often highly enriched with nutrients and oxygen. Colonization of this niche likely confers a significant fitness advantage in many cases. This study provides evidence that the cell surface adhesin known as a holdfast enables to partition to and colonize the air-liquid interface. Additional surface structures, including the flagellum and type IV pili, are important determinants of colonization and biofilm formation at this boundary. Considering that holdfast-like adhesins are broadly conserved in spp. and other members of the diverse class , these surface structures may function broadly to facilitate colonization of air-liquid boundaries in a range of ecological contexts, including freshwater, marine, and soil ecosystems.
在水生环境中， spp. 可以在液体和空气的交界处，即水层找到。我报告了一种研究在气液界面定殖和菌膜生物膜发育的时间特征的方法，并定义了细胞表面结构在这一过程中的作用。在这个界面上， 最初形成一层带有表面附着素的细胞，称为固着器。当从液体表面切除时，这单层强烈地附着在玻璃上。单层随后发育成一个富含称为玫瑰花结的杆状细胞簇的三维结构。随着这个菌膜成熟，它变得更具凝聚力，对玻璃表面的附着力降低。缺乏鞭毛的突变株不能有效地到达表面，缺乏 IV 型菌毛的菌株在三维菌膜的组织中表现出缺陷。不能合成固着器的菌株不能在空气和液体的边界处积累，也不能形成菌膜。相差图像支持这样一种模型，即固着器的功能是将细胞捕获在气液边界。与固着器不同，鞭毛和 IV 型菌毛都不是 将细胞分配到气液界面所必需的。虽然已经证实固着器能够附着在固体表面上，但这项研究提供了证据表明，固着器具有物理化学性质，允许非运动的母细胞分配到气液界面，并促进对这个微环境的定殖。在水生环境中，空气界面的边界通常富含营养物质和氧气。在许多情况下，定殖于这个小生境可能赋予了显著的适应优势。这项研究提供了证据表明，称为固着器的细胞表面附着素使 能够分配到气液界面并殖民该界面。包括鞭毛和 IV 型菌毛在内的其他表面结构是在这个边界处定殖和生物膜形成的重要决定因素。考虑到固着器样附着素在 spp. 和其他多样化类别的成员中广泛保守，这些表面结构可能在广泛的范围内发挥作用，以促进在各种生态背景下的气液边界的定殖，包括淡水、海洋和土壤生态系统。
