The Metabolite Vanillic Acid Regulates Acinetobacter baumannii Surface
Attachment
Abstract
The nosocomial bacterium Acinetobacter baumannii is protected
from antibiotic treatment by acquiring antibiotic resistances and by
forming biofilms. Cell attachment, one of the first steps in biofilm
formation, is normally induced by environmental metabolites. We
hypothesized that vanillic acid, the oxidized form of vanillin, a widely
available metabolite with antimicrobial properties, may play a role in
A. baumannii cell attachment. We first discovered that A.
baumannii actively breaks down VA through the evolutionarily conserved
vanABKP genes. These genes are under the control of the repressor
VanR, which we show binds directly to VanR binding sites within the
vanABKP genes bidirectional promoter. VA in turn counteracts VanR
inhibition. We identified a VanR binding site and searched for it
throughout the genome especially in pili encoding promoter genes. We
found a VanR binding site in the pilus encoding csu operon
promoter and showed that VanR binds specifically to it. As expected, a
strain lacking VanR overproduces Csu pili and makes robust biofilms. Our
study uncovers the role that VA plays in facilitating the attachment of
A. baumannii cells to surfaces, a crucial step in biofilm
formation. These findings provide valuable insights into a previously
obscure catabolic pathway with significant clinical implications.