Thioredoxin Modulates Cell Surface Hydrophobicity in Acinetobacter baumannii

Abstract

Acinetobacter baumannii, a Gram-negative coccobacillus, has become a prevalent nosocomial health threat affecting the majority of hospitals both in the U.S. and around the globe. Microbial cell surface hydrophobicity (CSH) has previously been correlated with virulence, uptake by immune cells, and attachment to epithelial cells. A mutant strain of A. baumannii (ΔtrxA) lacking the redox protein thioredoxin A was found to be more hydrophobic than its wild type (WT) and complemented counterparts, as measured by both Microbial Adhesion to Hydrocarbon (MATH) and salt aggregation. The hydrophobicity of the mutant could be abrogated through treatment with sodium cyanoborohydride (SCBH). This modulation correlated with reduction of disulfide bonds, as SCBH was able to reduce 5,5′-dithio-bis-[2-nitrobenzoic acid] and treatment with the known disulfide reducer, β-mercaptoethanol, also decreased ΔtrxA CSH. Additionally, the ΔtrxA mutant was more readily taken up than WT by J774 macrophages and this differential uptake could be abrogated though SCBH treatment. When partitioned into aqueous and hydrophobic phases, ΔtrxA recovered from the hydrophobic partition was phagocytosed more readily than from the aqueous phase further supporting the contribution of CSH to A. baumannii uptake by phagocytes. A second Gram-negative bacterium, Francisella novicida, also showed the association of TrxA deficiency (FnΔtrxA) with increased hydrophobicity and uptake by J774 cells. We previously have demonstrated that modification of the type IV pilus system (T4P) was associated with the A. baumannii ΔtrxA phenotype, and the Francisella FnΔtrxA mutant also was found to have a marked T4P deficiency. Interestingly, a F. novicida mutant lacking pilT also showed increased hydrophobicity over FnWT. Collective evidence presented in this study suggests that Gram-negative bacterial thioredoxin mediates CSH through multiple mechanisms including disulfide-bond reduction and T4P modulation.

Antibiofilm and antivirulence efficacy of myrtenol enhances the antibiotic susceptibility of Acinetobacter baumannii

“…Thus, MATH assay was done to assess the effect of EPS reduction on CSH of control and myrtenol treated cells. The result of MATH assay showed significant inhibition in the CSH of myrtenol treated sample which can be corroborated with the above theory and as well as another report 27 . The presence of flagella, pili and fimbriae in AB promotes the bacterial motility and biofilm formation.…”

A Tractable Drosophila Cell System Enables Rapid Identification of Acinetobacter baumannii Host Factors

“…We found that the pathogen successfully invaded mouse MH-S, TC-1, MLE-12, and Drosophila S2 cells (Figure 1A). However, the levels of bacterial invasion was significantly lower in these cells compared to J774 cells, a murine macrophage-like line that has been previously shown to be susceptible to invasion by A. baumannii (Asplund et al, 2013;May et al, 2019). To confirm our findings, we used gentamicin protection assays to analyze intracellular persistence or replication of the pathogen during a time course of infection.…”

Thioredoxin-mediated alteration of protein content and cytotoxicity of Acinetobacter baumannii outer membrane vesicles

“…14,35 Furthermore, TrxA-mediated modulation of bacterial surface hydrophobicity via disulfide bond reduction and regulation of type IV pili is a contributing factor to A. baumannii virulence. 36 The mechanism(s) for TrxAmediated differential OMV protein packaging remains to be determined; however, the TrxA-mediated alteration of cell hydrophobicity may play a role.…”