Characterization of RelA in Acinetobacter baumannii

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Molecular Biology

Background:

• RelA and SpoT proteins generate the signaling molecule (p)ppGpp in response to nutrient depletion, modulating bacterial cell physiology.
• Acinetobacter baumannii is a significant opportunistic pathogen, with increasing antibiotic resistance necessitating novel therapeutic approaches.

Purpose of the Study:

• To investigate the role of the RelA protein in Acinetobacter baumannii virulence and cellular processes.
• To characterize the phenotypes associated with the loss of RelA function in A. baumannii.

Main Methods:

• Identification of a relA ortholog (ABUW_3302) in A. baumannii strain AB5075.
• Construction and analysis of an in-frame deletion mutant (ΔrelA) to assess ppGpp production and associated phenotypes.
• Phenotypic characterization including colony morphology, motility assays, gene expression analysis, persister cell formation, and Galleria mellonella infection models.

Main Results:

• The ΔrelA mutant failed to produce ppGpp under amino acid starvation and was blocked in the switch from virulent opaque to avirulent translucent colony variants.
• ΔrelA mutants exhibited hypermotility, dependent on ABUW_1132 and AbaR, and increased expression of the acinetin 505 lipopeptide operon.
• Additional phenotypes included cell elongation, reduced persister cell formation, and decreased virulence in a Galleria mellonella model.

Conclusions:

• RelA plays a critical role in regulating virulence, colony phase variation, motility, and cell envelope properties in Acinetobacter baumannii.
• Targeting RelA and ppGpp production presents a potential therapeutic strategy to combat multidrug-resistant A. baumannii infections.