Presence of calcium-binding motifs in pilY1 homologs correlates with Ca-mediated twitching motility and evolutionary history across diverse bacteria

Abstract

Twitching motility, involving type IV pili, is essential for host colonization and virulence of many pathogenic bacteria. Studies of PilY1, a tip-associated type IV pili protein, indicate that PilY1 functions as a switch between pilus extension a retraction, resulting in twitching motility. Recent work detected a calcium-binding motif in PilY1 of some animal bacteri pathogens and demonstrated that binding of calcium to PilY1 with this motif regulates twitching. Though studies of PilY in non-animal pathogens are limited, our group demonstrated that twitching motility in the plant pathogen Xylella fastidiosa, which contains three PilY1 homologs, is increased by calcium supplementation. A study was conducted to investigate the phylogenetic relationship between multiple PilY1 homologs, the presence of calcium-binding motifs therein, and calcium-mediated twitching motility across diverse bacteria. Strains analyzed contained one to three PilY1 homologs, but phylogenetic analyses indicated that PilY1 homologs containing the calcium-binding motif Dx[DN]xDGxx are phylogenetically divergent from other PilY1 homologs. Plant-associated bacteria included in these analyses were the examined for a calcium-mediated twitching response. Results indicate that bacteria must have at least one PilY1 homolo containing the Dx[DN]xDGxxD motif to display a calcium-mediated increase in twitching motility, which likely relects a adaption to environmental calcium concentrations.