AspFlex: Molecular Tools to Study Gene Expression and Regulation in Acinetobacter baumannii

Identification of EppR, a Second Repressor of Error-Prone DNA Polymerase Genes in Acinetobacter baumannii

Acinetobacter baumannii is an opportunistic pathogen causing several infections that are increasingly difficult to treat due to its ability to rapidly gain antibiotic resistances. These resistances can arise due to mutations through the activity of error-prone DNA polymerases, such as DNA polymerase V (DNA Pol V) in response to DNA damage. The regulation of the DNA damage response (DDR) in A. baumannii is not completely understood; the regulation of genes encoding multiple copies of DNA Pol V is not fully characterized. Through genome-wide mutagenesis, we have identified a novel TetR-like family regulator of the umuDC and umuC genes, which we have named Error-prone polymerase regulator (EppR). We have found that EppR represses the expression of the genes encoding DNA Pol V and itself through direct binding to an EppR motif in their promoters. Lastly, we show that EppR also regulates UmuDAb, previously identified as a regulator of genes encoding DNA Pol V. These two gene products are functionally required to ensure regulation of the expression of the two umuDC, the two umuC genes as well as the regulators umuDAb and eppR genes. With these results, we propose a model in which multiple transcription factors regulate the expression of all these genes.

The metabolite vanillic acid regulates Acinetobacter baumannii surface attachment

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 (VA), the oxidized form of vanillin and a widely available metabolite, 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.

RecA levels modulate biofilm development in Acinetobacter baumannii

Infections caused by Acinetobacter baumannii, a Gram-negative opportunistic pathogen, are difficult to eradicate due to the bacterium's propensity to quickly gain antibiotic resistances and form biofilms, a protective bacterial multicellular community. The A. baumannii DNA damage response (DDR) mediates the antibiotic resistance acquisition and regulates RecA in an atypical fashion; both RecALow and RecAHigh cell types are formed in response to DNA damage. The findings of this study demonstrate that the levels of RecA can influence formation and dispersal of biofilms. RecA loss results in surface attachment and prominent biofilms, while elevated RecA leads to diminished attachment and dispersal. These findings suggest that the challenge to treat A. baumannii infections may be explained by the induction of the DDR, common during infection, as well as the delicate balance between maintaining biofilms in low RecA cells and promoting mutagenesis and dispersal in high RecA cells. This study underscores the importance of understanding the fundamental biology of bacteria to develop more effective treatments for infections.