Thioredoxin Modulates Cell Surface Hydrophobicity in Acinetobacter baumannii.

Area of Science:

• Microbiology
• Cell Biology
• Immunology

Background:

• Acinetobacter baumannii is a significant nosocomial pathogen.
• Microbial cell surface hydrophobicity (CSH) correlates with bacterial virulence and host cell interactions.
• Thioredoxin A (TrxA) is a redox protein involved in cellular processes.

Purpose of the Study:

• To investigate the role of thioredoxin A in Acinetobacter baumannii cell surface hydrophobicity.
• To determine the impact of altered hydrophobicity on bacterial uptake by macrophages.
• To explore the mechanisms by which TrxA influences CSH and bacterial-host interactions.

Main Methods:

• Generated and characterized an Acinetobacter baumannii ΔtrxA mutant.
• Assessed cell surface hydrophobicity using Microbial Adhesion to Hydrocarbon (MATH) assay and salt aggregation.
• Investigated the effect of sodium cyanoborohydride (SCBH) and β-mercaptoethanol on CSH.
• Quantified bacterial uptake by J774 macrophages.
• Analyzed the type IV pilus system (T4P) in wild-type and mutant strains.

Main Results:

• The Acinetobacter baumannii ΔtrxA mutant exhibited significantly increased CSH compared to wild-type.
• Increased hydrophobicity of the ΔtrxA mutant correlated with enhanced uptake by J774 macrophages.
• Sodium cyanoborohydride treatment reduced ΔtrxA hydrophobicity and abrogated differential macrophage uptake.
• TrxA deficiency in both Acinetobacter baumannii and Francisella novicida led to increased CSH and phagocytosis.
• T4P deficiency was observed in ΔtrxA mutants of both bacterial species, suggesting a role in CSH modulation.

Conclusions:

• Thioredoxin A plays a crucial role in regulating Gram-negative bacterial cell surface hydrophobicity.
• Reduced CSH, mediated by TrxA, enhances bacterial interaction with and uptake by phagocytic cells.
• Disulfide bond reduction and type IV pilus system modulation are key mechanisms by which TrxA influences CSH.