Chemosensory diversity across the order Vibrionales reveals a conserved core and three accessory signalling systems

Chemosensory systems (CSSs) are multi-protein assemblies regulating bacterial motility and diverse alternative cellular functions. Despite extensive study of chemotaxis in Vibrio cholerae, a comprehensive evolutionary analysis of CSSs across order Vibrionales has been lacking. Using 116 curated representative genomes across 28 Vibrio clades and ~10,000 RefSeq/metagenome-assembled genomes, we characterized the chemosensory toolkit of Vibrionales. CheA-based phylogenetics, CSS architecture, sequence similarity networks, structural comparisons, and synteny analysis identified four discrete CSS types: F6, F7, F9, and an experimentally unexplored F8. F6 is universally conserved on chromosome I and essential for flagellar motility (chemotaxis), while F7, F8, and F9 show patchy, replicon-flexible distributions reflecting lineage-specific retention or horizontal acquisition. F6, F7, and F8 were vertically inherited from Gammaproteobacteria and retained in selected species, whereas F9 was horizontally acquired from Alphaproteobacteria in only selected species. Structural analysis further reveals conserved CheA folds despite sequence divergence, with lineage-specific insertions in F8 and F9 CheA proteins. Collectively, this study reveals a two-tier chemosensory architecture within order Vibrionales: 1) a chromosomally stable F6 motility core under purifying selection, 2) overlaid by dynamically evolving F7, F8, and F9 accessory systems, wherein multipartite genome organization might serve as an evolutionary key for sensory innovation in order Vibrionales, enabling rapid niche adaptation without compromising core chemotactic fidelity.