O'Rear J, Alberti L, Harshey R M
Department of Microbiology, University of Texas, Austin 78712.
J Bacteriol. 1992 Oct;174(19):6125-37. doi: 10.1128/jb.174.19.6125-6137.1992.
Serratia marcescens exists in two cell forms and displays two kinds of motility depending on the type of growth surface encountered (L. Alberti and R. M. Harshey, J. Bacteriol. 172:4322-4328, 1990). In liquid medium, the bacteria are short rods with few flagella and show classical swimming behavior. Upon growth on a solid surface (0.7 to 0.85% agar), they differentiate into elongated, multinucleate, copiously flagellated forms that swarm over the agar surface. The flagella of swimmer and swarmer cells are composed of the same flagellin protein. We show in this study that disruption of hag, the gene encoding flagellin, abolishes both swimming and swarming motility. We have used transposon mini-Mu lac kan to isolate mutants of S. marcescens defective in both kinds of motility. Of the 155 mutants obtained, all Fla- mutants (lacking flagella) and Mot- mutants (paralyzed flagella) were defective for both swimming and swarming, as expected. All Che- mutants (chemotaxis defective) were also defective for swarming, suggesting that an intact chemotaxis system is essential for swarming. About one-third of the mutants were specifically affected only in swarming. Of this class, a large majority showed active "swarming motility" when viewed through the microscope (analogous to the active "swimming motility" of Che- mutants) but failed to show significant movement away from the site of initial inoculation on a macroscopic scale. These results suggest that bacteria swarming on a solid surface require many genes in addition to those required for chemotaxis and flagellar function, which extend the swarming movement outward. We also show in this study that nonflagellate S. marcescens is capable of spreading rapidly on low-agar media.
粘质沙雷氏菌存在两种细胞形态，并根据所遇到的生长表面类型表现出两种运动方式（L. 阿尔贝蒂和R. M. 哈谢，《细菌学杂志》172:4322 - 4328，1990年）。在液体培养基中，细菌是带有少量鞭毛的短杆状，表现出典型的游动行为。在固体表面（0.7%至0.85%琼脂）上生长时，它们会分化成细长的、多核的、有大量鞭毛的形态，并在琼脂表面成群游动。游动细胞和群体游动细胞的鞭毛由相同的鞭毛蛋白组成。我们在本研究中表明，编码鞭毛蛋白的基因hag的破坏会消除游动和群体游动运动能力。我们使用转座子mini - Mu lac kan来分离在两种运动能力方面有缺陷的粘质沙雷氏菌突变体。在所获得的155个突变体中，正如预期的那样，所有Fla - 突变体（缺乏鞭毛）和Mot - 突变体（鞭毛麻痹）在游动和群体游动方面都有缺陷。所有Che - 突变体（趋化性缺陷）在群体游动方面也有缺陷，这表明完整的趋化系统对于群体游动至关重要。大约三分之一的突变体仅在群体游动方面受到特异性影响。在这一类中，绝大多数在显微镜下观察时表现出活跃的“群体游动运动”（类似于Che - 突变体的活跃“游动运动”），但在宏观尺度上未能显示出明显远离初始接种位点的移动。这些结果表明，在固体表面群体游动的细菌除了趋化和鞭毛功能所需的基因外，还需要许多其他基因，这些基因可使群体游动运动向外扩展。我们在本研究中还表明，无鞭毛的粘质沙雷氏菌能够在低琼脂培养基上快速扩散。
