Flagella occur on many prokaryotes, which primarily propel cells to move from detrimental to favorable environments. A variety of species-specific flagellation patterns have been identified. Although it is presumed that for each of these flagellated microorganisms, an evolutionarily fixed flagellation pattern is favored under the normal living conditions, direct evidence is lacking. Here, we use Shewanella oneidensis, a rod-shaped Gram-negative bacterium with a monotrichous polar flagellum (MR-1, the wild-type), as a research model. The investigation has been enabled by multiple mutants with diverse flagellation patterns that had been generated by removing FlhF and FlhG proteins that control flagellar location and number, respectively. Growth assays, as a measure of fitness, revealed that the wild-type strain predominated in spreading on swim plates and in pellicles which form at the air–liquid interface. However, under the pellicles where oxygen is limited, both aflagellated and monotrichous lateral strains showed similar increase in fitness, whereas strains with multiple flagella were less competitive. Moreover, under shaking culturing conditions, the aflagellated strain outcompeted all other strains, including the wild-type, suggesting that cells devoid of flagella would be more likely enriched upon agitation. Overall, these data support the presumption that the monotrichous polar flagellum, as evolutionarily fixed in the wild-type strain, is optimal for the growth fitness of S. oneidensis over any other mutants under most test conditions. However, upon specific changes of environmental conditions, another form could come to predominate. These findings provide insight into the impacts of flagellation patterns and function on bacterial adaptation to differing environments.

中文翻译：

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Shewanella oneidensis的鞭毛对不同环境中细菌适应性的影响

鞭毛存在于许多原核生物中，主要推动细胞从有害环境移动到有利环境。已经确定了多种物种特定的鞭毛模式。尽管假设对于这些鞭毛微生物中的每一种，在正常生活条件下都有利于进化固定的鞭毛模式，但缺乏直接证据。在这里，我们使用 Shewanella oneidensis，一种杆状革兰氏阴性细菌，具有单发极鞭毛（MR-1，野生型），作为研究模型。通过去除分别控制鞭毛位置和数量的 FlhF 和 FlhG 蛋白，具有不同鞭毛模式的多个突变体使这项研究成为可能。生长测定，作为健康的衡量标准，揭示了野生型菌株在游泳板上和在气液界面形成的薄膜中占主导地位。然而，在氧气有限的薄膜下，有鞭毛的和单毛的侧向菌株的适应性增加相似，而具有多个鞭毛的菌株的竞争力较差。此外，在振荡培养条件下，鞭毛菌株胜过所有其他菌株，包括野生型，这表明缺乏鞭毛的细胞在搅拌时更有可能富集。总体而言，这些数据支持这样的假设，即在进化上固定在野生型菌株中的单发极鞭毛在大多数测试条件下对于 S. oneidensis 的生长适应性优于任何其他突变体。但是，随着环境条件的具体变化，另一种形式可能会占主导地位。这些发现提供了对鞭毛模式和功能对细菌适应不同环境的影响的深入了解。