School of Molecular & Cell Biology, University of the Witwatersrand, Wits, 2050, South Africa.
Centre for Microbial Ecology and Genomics, University of Pretoria, Pretoria, 0002, South Africa.
BMC Genomics. 2020 Sep 29;21(1):670. doi: 10.1186/s12864-020-07085-w.
Flagellar motility is an efficient means of movement that allows bacteria to successfully colonize and compete with other microorganisms within their respective environments. The production and functioning of flagella is highly energy intensive and therefore flagellar motility is a tightly regulated process. Despite this, some bacteria have been observed to possess multiple flagellar systems which allow distinct forms of motility.
Comparative genomic analyses showed that, in addition to the previously identified primary peritrichous (flag-1) and secondary, lateral (flag-2) flagellar loci, three novel types of flagellar loci, varying in both gene content and gene order, are encoded on the genomes of members of the order Enterobacterales. The flag-3 and flag-4 loci encode predicted peritrichous flagellar systems while the flag-5 locus encodes a polar flagellum. In total, 798/4028 (~ 20%) of the studied taxa incorporate dual flagellar systems, while nineteen taxa incorporate three distinct flagellar loci. Phylogenetic analyses indicate the complex evolutionary histories of the flagellar systems among the Enterobacterales.
Supernumerary flagellar loci are relatively common features across a broad taxonomic spectrum in the order Enterobacterales. Here, we report the occurrence of five (flag-1 to flag-5) flagellar loci on the genomes of enterobacterial taxa, as well as the occurrence of three flagellar systems in select members of the Enterobacterales. Considering the energetic burden of maintaining and operating multiple flagellar systems, they are likely to play a role in the ecological success of members of this family and we postulate on their potential biological functions.
鞭毛运动是一种有效的运动方式，使细菌能够成功地在其所处的环境中定殖并与其他微生物竞争。鞭毛的产生和功能需要大量的能量，因此鞭毛运动是一个受到严格调控的过程。尽管如此，一些细菌已经被观察到拥有多个鞭毛系统，从而允许不同形式的运动。
比较基因组分析表明，除了先前鉴定的初级周生（flag-1）和次级、侧向（flag-2）鞭毛基因座外，肠杆菌目中的一些成员的基因组上还编码了三种新型的鞭毛基因座，其在基因内容和基因顺序上都有所不同。flag-3 和 flag-4 基因座编码预测的周生鞭毛系统，而 flag-5 基因座编码一个极鞭毛。总的来说，798/4028（~20%）的研究类群包含双鞭毛系统，而 19 个类群包含三个不同的鞭毛基因座。系统发育分析表明，肠杆菌目中的鞭毛系统具有复杂的进化历史。
超数鞭毛基因座在肠杆菌目广泛的分类范围内是相对常见的特征。在这里，我们报告了在肠杆菌类群的基因组上出现了五个（flag-1 到 flag-5）鞭毛基因座，以及在肠杆菌目中的某些成员中出现了三个鞭毛系统。考虑到维持和操作多个鞭毛系统的能量负担，它们可能在该家族成员的生态成功中发挥作用，我们推测了它们的潜在生物学功能。
