Novel role of bacterial lipocalins in cell protection against antibiotic-induced membrane lipid peroxidation

Abstract

Environmental and pathogenic Gram-negative bacteria are exposed to lipid peroxidation emerging from oxidative stress conditions. However, the mechanism to survive this stress is essentially unknown. The opportunistic pathogen Burkholderia cenocepacia encodes three genes that are upregulated under oxidative stress conditions such as sub-lethal concentration of antibiotic and superoxide ion stress. One of these genes, bcnA, encodes a periplasmic protein from the lipocalin family, which is usually associated with a gene encoding a cytochrome b561 inner-transmembrane protein that we named lcoA; this synteny is conserved in the majority of the β-proteobacteria. Compared to the wild type, mutants lacking these proteins and psrA, a gene encoding a cytoplasmic aldehyde reductase that reduces toxic aldehydes, are more susceptible to bactericidal antibiotics and produce more lipid peroxidation by-products. Fluorescent microscopy analysis using a probe that interacts with lipid peroxyl radicals shows an accumulation of these molecules at the bacterial cell poles and septum. Additionally, using a dye that interacts with anionic phospholipids, we found that peroxidation is associated with a redistribution of anionic phospholipids in the membrane. From this, we conclude that BcnA, LcoA, and PsrA are components of an evolutionarily conserved, previously obscure peroxidation detoxification system that protects the bacterial cell envelope from lipid peroxyl radicals.

Thesis is embargoed until 31 December 2025.

Date of Award	Dec 2023
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Northern Ireland Department for the Economy
Supervisor	Miguel A. Valvano (Supervisor) & Guillermo Lopez Campos (Supervisor)