Flagella by numbers: comparative genomic analysis of the supernumerary flagellar systems among the Enterobacterales
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RESEARCH ARTICLE
Open Access
Flagella by numbers: comparative genomic analysis of the supernumerary flagellar systems among the Enterobacterales Pieter De Maayer1* , Talia Pillay1 and Teresa A. Coutinho2
Abstract Background: 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. Results: 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. Conclusions: 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. Keywords: Enterobacterales, Supernumerary flagella, Flag, Evolution, Motility
Background Flagella are complex structures that provide bacteria with an effective means of carrying out swimming (movement of single bacterial cells in liquid environments) and swarming (coordinated mobility of bacterial population on semi-solid or solid surfaces) movements [1]. Furthermore, they participate in biofilm formation, * Correspondence: [email protected] 1 School of Molecular & Cell Biology, University of the Witwatersrand, Wits 2050, South Africa Full list of author information is available at the end of the article
adhesion to surfaces and host cell invasion [2–4]. As such, flagella provide bacteria with a considerable competitive advantage over non-motile microorganisms occupying the same ecological niche and > 80% of known bacterial species are known to produce and maintain these structures [2, 3]. The basic structure of the flagellum is relatively well conserved among the flagellate bacteria, comprising of a basal body, hook and flagellar filament [5]. However, extensive diversity occurs within an
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