Atypical thioredoxin Patrx2 enhances alginate production in mucoid Pseudomonas 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 plays a crucial role 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, which we attributed to its catalytic activity in a C34S variant. The study of Patrx2, an atypical thioredoxin expressed within an alginate biofilm, underscores the importance of redox regulation in adaptation mechanisms. Patrx2s involvement in alginate biosynthesis opens new pathway for inhibiting biofilm synthesis. HighlightsO_LIThe patrx2 gene is regulated by the alternative sigma factor AlgU C_LIO_LIPatrx2 is strongly produced in mucoid P. aeruginosa C_LIO_LIPatrx2 is an atypical thioredoxin with disulfide isomerase activity C_LIO_LIPatrx2 impacts alginate production in the mucoid P. aeruginosa mucA22 strain, likely through redox regulation of alginate biosynthesis. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=128 SRC="FIGDIR/small/667166v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@14f304forg.highwire.dtl.DTLVardef@1ecc15eorg.highwire.dtl.DTLVardef@8b18d9org.highwire.dtl.DTLVardef@c71b7_HPS_FORMAT_FIGEXP M_FIG C_FIG