Comparative genomic analysis of the secondary flagellar (flag-2) system in the order Enterobacterales

Pieter De Maayer,Teresa A Coutinho,Talia Pillay

doi:10.1186/s12864-020-6529-9

Pieter De Maayer, Teresa A Coutinho + Show 1 more

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https://doi.org/10.1186/s12864-020-6529-9

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Abstract

BackgroundThe order Enterobacterales encompasses a broad range of metabolically and ecologically versatile bacterial taxa, most of which are motile by means of peritrichous flagella. Flagellar biosynthesis has been linked to a primary flagella locus, flag-1, encompassing ~ 50 genes. A discrete locus, flag-2, encoding a distinct flagellar system, has been observed in a limited number of enterobacterial taxa, but its function remains largely uncharacterized.ResultsComparative genomic analyses showed that orthologous flag-2 loci are present in 592/4028 taxa belonging to 5/8 and 31/76 families and genera, respectively, in the order Enterobacterales. Furthermore, the presence of only the outermost flag-2 genes in many taxa suggests that this locus was far more prevalent and has subsequently been lost through gene deletion events. The flag-2 loci range in size from ~ 3.4 to 81.1 kilobases and code for between five and 102 distinct proteins. The discrepancy in size and protein number can be attributed to the presence of cargo gene islands within the loci. Evolutionary analyses revealed a complex evolutionary history for the flag-2 loci, representing ancestral elements in some taxa, while showing evidence of recent horizontal acquisition in other enterobacteria.ConclusionsThe flag-2 flagellar system is a fairly common, but highly variable feature among members of the Enterobacterales. Given the energetic burden of flagellar biosynthesis and functioning, the prevalence of a second flagellar system suggests it plays important biological roles in the enterobacteria and we postulate on its potential role as locomotory organ or as secretion system.

Highlights

The order Enterobacterales encompasses a broad range of metabolically and ecologically versatile bacterial taxa, most of which are motile by means of peritrichous flagella
Key to the ecological success of enterobacteria is their capacity for motility, which is largely mediated by flagella, specialized surface structures that allow bacterial cells to
The flag-2 locus is widespread among the Enterobacterales The finished and draft genomes of 4028 bacterial strains encompassing the taxonomic diversity of the order

Summary

Introduction

The order Enterobacterales encompasses a broad range of metabolically and ecologically versatile bacterial taxa, most of which are motile by means of peritrichous flagella. Recent phylogenomic re-evaluation of the sole family in this order, the Enterobacteriaceae, has resulted in its division into eight distinct families [1] Members of this order can be found in a diverse range of environments including air, soil, water and in association with plant and animal hosts, and include some of the most important pathogens of these hosts [2]. The filament is the longest, surface-exposed, component of the bacterial flagellum and is composed of approximately 20,000 subunits of the major structural protein [6, 9]. This filament serves as a propeller, which converts the motor into thrust to propel the bacterial cell [9]

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