Presence of calcium-binding motifs in PilY1 homologs correlates with Ca-mediated twitching motility and evolutionary history across diverse bacteria.

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 and retraction, resulting in twitching motility. Recent work detected a calcium-binding motif in PilY1 of some animal bacterial pathogens and demonstrated that binding of calcium to PilY1 with this motif regulates twitching. Though studies of PilY1 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]xDGxxD are phylogenetically divergent from other PilY1 homologs. Plant-associated bacteria included in these analyses were then examined for a calcium-mediated twitching response. Results indicate that bacteria must have at least one PilY1 homolog containing the Dx[DN]xDGxxD motif to display a calcium-mediated increase in twitching motility, which likely reflects an adaption to environmental calcium concentrations.