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
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.