Abstract
Here we present an examination of type IV pilus genes associated with competence and twitching in the bacterium Acinetobacter baylyi (strain ADP1, BD413). We used bioinformatics to identify potential competence and twitching genes and their operons. We measured the competence and twitching phenotypes of the bioinformatically-identified genes. These results demonstrate that competence and twitching in A. baylyi both rely upon a core of the same type IV pilus proteins. The core includes the inner membrane assembly platform (PilC), a periplasmic assemblage connecting the inner membrane assembly platform to the secretin (ComM), a secretin (ComQ) and its associated pilotin (PilF) that assists with secretin assembly and localization, both cytoplasmic pilus retraction ATPases (PilU, PilT), and pilins (ComP, ComB, PilX). Proteins not needed for both competence and twitching are instead found to specialize in either of the two traits. The pilins are varied in their specialization with some required for either competence (FimT) and others for twitching (ComE). The protein that transports DNA across the inner membrane (ComA) specializes in competence, while signal transduction proteins (PilG, PilS, and PilR) specialize in twitching. Taken together our results suggest that the function of accessory proteins should not be based on homology alone. In addition the results suggest that in A. baylyi the mechanisms of natural transformation and twitching are mediated by the same set of core Type IV pilus proteins with distinct specialized proteins required for each phenotype. Finally, since competence requires multiple pilins as well as both pilus retraction motors PilU and PilT, this suggests that A. baylyi employs a pilus in natural transformation.
Highlights
Natural transformation is the ability of physiologically competent bacteria to internalize exogenous DNA and incorporate it into their own genomes
Type IV pilus genes, natural transformation, and twitching motility in Acinetobacter baylyi are exclusively competent during twitching on a surface, so there may be cases where pilus retraction drags the cell forward, fortuitously allowing it to collide with DNA in the surrounding environment [35]
In ADP1 several type IV pilus genes are required for competence [50]
Summary
Natural transformation is the ability of physiologically competent bacteria to internalize exogenous DNA and incorporate it into their own genomes. Type IV pilus genes, natural transformation, and twitching motility in Acinetobacter baylyi are exclusively competent during twitching on a surface, so there may be cases where pilus retraction drags the cell forward, fortuitously allowing it to collide with DNA in the surrounding environment [35]. We found that in A. baylyi competence and twitching both rely upon a core of the same type IV pilus proteins; there are proteins, including pilins, specialized in one functionality or the other These findings suggest that the mechanism of natural transformation is likely very similar to that of twitching and that the function of accessory proteins in any given organism may not be predictable based on homology alone
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