Abstract
BackgroundFlagellar 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.ResultsComparative 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.ConclusionsSupernumerary 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.
Highlights
Flagellar motility is an efficient means of movement that allows bacteria to successfully colonize and compete with other microorganisms within their respective environments
The Enterobacterales encode five distinct flagellar systems The complete and draft genomes of 4082 taxa belonging to the order Enterobacterales were screened for the presence of additional flagellar loci by performing tBlastN analysis of the full complement of complete protein sequences required for the synthesis of the flag-1 and flag-2 flagella of E. coli K-12 strain MG1655 (47 proteins) and E. coli 042 (38 proteins), respectively, against the genome sequences
The protein complements encoded by the remaining additional flagellar loci, along with taxonomically representative flag-1 and flag-2 datasets were compared
Summary
Flagellar motility is an efficient means of movement that allows bacteria to successfully colonize and compete with other microorganisms within their respective environments. 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] They participate in biofilm formation, The basic structure of the flagellum is relatively well conserved among the flagellate bacteria, comprising of a basal body, hook and flagellar filament [5]. A limited number of bacterial taxa produce dual flagellar systems encoded by distinct sets of genes present on the genome This trait has been most widely studied in Vibrio and Aeromonas spp., which possess both a polar flagellum as well as several lateral (peritrichous) flagella [2, 6,7,8,9]. Bacteria that are capable of producing dual flagellar systems tightly regulate the production of polar and lateral flagella [9, 10]
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