# Atypical thioredoxin Patrx2 enhances alginate production in mucoid Pseudomonasaeruginosa

## TL;DR

A unique thioredoxin called Patrx2 in Pseudomonas aeruginosa helps increase alginate production in biofilms, which is important for the bacteria's adaptation.

## Contribution

Patrx2 is a novel atypical thioredoxin with disulfide isomerase activity that influences alginate production in mucoid P. aeruginosa.

## Key findings

- Patrx2 is regulated by the sigma factor AlgU and is strongly expressed in mucoid P. aeruginosa.
- Patrx2 has disulfide isomerase activity and structural features similar to eukaryotic protein disulfide isomerases.
- Patrx2 is important for alginate production in mucoid strains of P. aeruginosa.

## Abstract

Pseudomonas aeruginosa, an opportunistic human pathogen, is known for its ability to respond and adapt to its environment, employing intricate adaptation mechanisms that can lead to the formation of complex biofilms. Redox processes play a pivotal role in bacterial adaptation mechanisms. The cytoplasm of most organisms is recognized for maintaining a reducing environment through thiol-disulfide oxidoreductases. In Pseudomonas aeruginosa, we have identified an unusual cytoplasmic thioredoxin named Patrx2. What sets Patrx2 apart is its active site, which contains a consensus sequence, CGHC, identical to the characteristic motif of protein disulfide isomerases (PDIs) found in eukaryotic cells. Our investigations have unveiled that Patrx2, unlike canonical thioredoxins, exhibits disulfide isomerase activity in vitro and displays physicochemical properties, as well as a structural conformation of its catalytic site, reminiscent of PDIs. Using a mutant transposon library, we found that the expression of patrx2 is regulated by the alternative sigma factor AlgU, which is implicated in the formation of alginate biofilms in P. aeruginosa. We further demonstrated strong patrx2 expression in a mucoid strain we constructed, carrying the clinically relevant mucA22 mutation frequently found in cystic fibrosis patients. Furthermore, our results showed a significant decrease in alginate synthesis in a patrx2 mutant in this mucoid strain, this effect was also observed in the C34S catalytic variant, suggesting a role for Patrx2's catalytic site in this phenotype. The study of Patrx2, an atypical thioredoxin expressed within an alginate biofilm, underscores the importance of redox regulation in adaptation mechanisms. The induction of Patrx2's expression in alginate-producing biofilms highlights its potential relevance in redox-regulated adaptation mechanisms.

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•The patrx2 gene is regulated by the alternative sigma factor AlgU.•Patrx2 is strongly produced in mucoid P. aeruginosa.•Patrx2 is an atypical thioredoxin with disulfide isomerase activity.•Patrx2 impacts alginate production in the mucoid P. aeruginosa mucA22 strain.

The patrx2 gene is regulated by the alternative sigma factor AlgU.

Patrx2 is strongly produced in mucoid P. aeruginosa.

Patrx2 is an atypical thioredoxin with disulfide isomerase activity.

Patrx2 impacts alginate production in the mucoid P. aeruginosa mucA22 strain.