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PmrA-PmrB-regulated genes necessary for 4-aminoarabinose lipid A modification and polymyxin resistance
Abstract:
Antimicrobial peptides are distributed throughout the animal kingdom and are a key component of innate immunity. Salmonella typhimurium regulates mechanisms of resistance to cationic antimicrobial peptides through the two-component systems PhoP-PhoQ and PmrA-PmrB. Polymyxin resistance is encoded by the PmrA-PmrB regulon, whose products modify the lipopolysaccharide (LPS) core and lipid A regions with ethanolamine and add aminoarabinose to the 4' phosphate of lipid A. Two PmrA-PmrB-regulated S. typhimurium loci (pmrE and pmrF) have been identified that are necessary for resistance to polymyxin and for the addition of aminoarabinose to lipid A. One locus, pmrE, contains a single gene previously identified as pagA (or ugd) that is predicted to encode a UDP-glucose dehydrogenase. The second locus, pmrF, is the second gene of a putative operon predicted to encode seven proteins, some with similarity to glycosyltransferases and other complex carbohydrate biosynthetic enzymes. Genes immediately flanking this putative operon are also regulated by PmrA-PmrB and/or have been associated with S. typhimurium polymyxin resistance. This work represents the first identification of non-regulatory genes necessary for modification of lipid A and subsequent antimicrobial peptide resistance, and provides support for the hypothesis that lipid A aminoarabinose modification promotes resistance to cationic antimicrobial peptides.
Insights
Salmonella typhimurium develops resistance to antimicrobial peptides by modifying its lipopolysaccharide (LPS) layer. This study identifies new genes, pmrE and pmrF, crucial for LPS modification and polymyxin resistance.
Area of Science:
- Microbiology
- Immunology
- Biochemistry
Background:
- Antimicrobial peptides are vital components of innate immunity across the animal kingdom.
- Salmonella typhimurium employs two-component systems (PhoP-PhoQ and PmrA-PmrB) to resist cationic antimicrobial peptides.
- Polymyxin resistance in S. typhimurium involves modifications to lipopolysaccharide (LPS) by the PmrA-PmrB regulon, including the addition of aminoarabinose to lipid A.
Purpose of the Study:
- To identify non-regulatory genes in Salmonella typhimurium essential for lipid A modification.
- To elucidate the genetic basis of resistance to cationic antimicrobial peptides, specifically polymyxin.
- To understand the role of pmrE and pmrF loci in LPS modification and antimicrobial peptide resistance.
Main Methods:
- Genetic analysis of Salmonella typhimurium strains.
- Identification and characterization of PmrA-PmrB-regulated loci (pmrE and pmrF).
- Biochemical analysis of lipopolysaccharide (LPS) modifications, including aminoarabinose addition to lipid A.
Main Results:
- Two S. typhimurium loci, pmrE and pmrF, were identified as necessary for polymyxin resistance.
- pmrE contains the pagA (ugd) gene, encoding UDP-glucose dehydrogenase.
- pmrF is part of a putative operon encoding proteins involved in complex carbohydrate biosynthesis, facilitating aminoarabinose addition to lipid A.
Conclusions:
- The study identifies novel non-regulatory genes (pmrE, pmrF) critical for antimicrobial peptide resistance in S. typhimurium.
- Lipid A modification with aminoarabinose is confirmed as a mechanism promoting resistance to cationic antimicrobial peptides.
- These findings advance the understanding of bacterial resistance mechanisms and innate immunity.