Peptidoglycan-Binding Anchor Is a Pseudomonas aeruginosa OmpA Family Lipoprotein With Importance for Outer Membrane Vesicles, Biofilms, and the Periplasmic Shape

Magnus Paulsson; Kasper Nørskov Kragh; Yu-Ching Su; Linda Sandblad; Birendra Singh; Thomas Bjarnsholt; Kristian Riesbeck

doi:10.3389/fmicb.2021.639582

Peptidoglycan-Binding Anchor Is a Pseudomonas aeruginosa OmpA Family Lipoprotein With Importance for Outer Membrane Vesicles, Biofilms, and the Periplasmic Shape

Front Microbiol. 2021 Feb 25:12:639582. doi: 10.3389/fmicb.2021.639582. eCollection 2021.

Authors

Magnus Paulsson^{1

2}, Kasper Nørskov Kragh³, Yu-Ching Su¹, Linda Sandblad⁴, Birendra Singh¹, Thomas Bjarnsholt^{3

5}, Kristian Riesbeck¹

Affiliations

¹ Clinical Microbiology, Department of Translational Medicine, Faculty of Medicine, Lund University, Malmö, Sweden.
² Division for Infectious Diseases, Skåne University Hospital, Lund, Sweden.
³ Faculty of Health and Medical Sciences, Costerton Biofilm Center, University of Copenhagen, Copenhagen, Denmark.
⁴ Department of Integrative Medical Biology, Umeå University, Umeå, Sweden.
⁵ Department of Clinical Microbiology, Copenhagen University Hospital, Copenhagen, Denmark.

Abstract

The outer membrane protein A (OmpA) family contains an evolutionary conserved domain that links the outer membrane in Gram-negative bacteria to the semi-rigid peptidoglycan (PG) layer. The clinically significant pathogen Pseudomonas aeruginosa carries several OmpA family proteins (OprF, OprL, PA0833, and PA1048) that share the PG-binding domain. These proteins are important for cell morphology, membrane stability, and biofilm and outer membrane vesicle (OMV) formation. In addition to other OmpAs, in silico analysis revealed that the putative outer membrane protein (OMP) with gene locus PA1041 is a lipoprotein with an OmpA domain and, hence, is a potential virulence factor. This study aimed to evaluate PA1041 as a PG-binding protein and describe its effect on the phenotype. Clinical strains were confirmed to contain the lipoprotein resulting from PA1041 expression with Western blot, and PG binding was verified in enzyme-linked immunosorbent assay (ELISA). By using a Sepharose bead-based ELISA, we found that the lipoprotein binds to meso-diaminopimelic acid (mDAP), an amino acid in the pentapeptide portion of PGs. The reference strain PAO1 and the corresponding transposon mutant PW2884 devoid of the lipoprotein were examined for phenotypic changes. Transmission electron microscopy revealed enlarged periplasm spaces near the cellular poles in the mutant. In addition, we observed an increased release of OMV, which could be confirmed by nanoparticle tracking analysis. Importantly, mutants without the lipoprotein produced a thick, but loose and unorganized, biofilm in flow cells. In conclusion, the lipoprotein from gene locus PA1041 tethers the outer membrane to the PG layer, and mutants are viable, but display severe phenotypic changes including disordered biofilm formation. Based upon the phenotype of the P. aeruginosa PW2884 mutant and the function of the protein, we designate the lipoprotein with locus tag PA1041 as "peptidoglycan-binding anchor" (Pba).

Keywords: OMV; Pseudomonas aeruginosa; biofilm; lipoproteins; outer membrane vesicles; peptidoglycan.