Bacteroidetocins Target the Essential Outer Membrane Protein BamA of Bacteroidales Symbionts and Pathogens
Open Access
- 26 October 2021
- journal article
- research article
- Published by American Society for Microbiology in mBio
- Vol. 12 (5), e0228521
- https://doi.org/10.1128/mbio.02285-21
Abstract
Bacteroidetocins are a family of antibacterial peptide toxins that are produced by and target members of the phylum Bacteroidetes. To date, 19 bacteroidetocins have been identified, and four have been tested and shown to kill diverse Bacteroidales species (M. J. Coyne, N. Bechon, L. M. Matano, V. L. McEneany, et al., Nat Commun 10:3460, 2019, https://doi.org/10.1038/s41467-019-11494-1). Here, we identify the target and likely mechanism of action of the bacteroidetocins. We selected seven spontaneous mutants of four different genera, all resistant to bacteroidetocin A (Bd-A) and found that all contained mutations in a single gene, bamA. Construction of three of these bamA mutants in the wild-type (WT) strains confirmed they confer resistance to Bd-A as well as to other bacteroidetocins. We identified an aspartate residue of BamA at the beginning of exterior loop 3 (eL3) that, when altered, renders strains resistant to Bd-A. Analysis of a panel of diverse Bacteroidales strains showed a correlation between the presence of this aspartate residue and Bd-A sensitivity. Fluorescence microscopy and transmission electron microscopy (TEM) analysis of Bd-A-treated cells showed cellular morphological changes consistent with a BamA defect. Transcriptomic analysis of Bd-A-treated cells revealed gene expression changes indicative of cell envelope stress. Studies in mice revealed that bacteroidetocin-resistant mutants are out-competed by their WT strain in vivo. Analyses of longitudinal human gut isolates showed that bamA mutations leading to bacteroidetocin resistance do not become fixed in the human gut, even in bacteroidetocin-producing strains and nonproducing coresident strains. Together, these data lend further support to the applicability of the bacteroidetocins as therapeutic peptides in the treatment of maladies involving Bacteroidales species. IMPORTANCE The bacteroidetocins are a newly discovered class of bacteriocins specific to Bacteroidetes with a spectrum of targets extending from symbiotic gut Bacteroides, Parabacteroides, and Prevotella species to pathogenic oral and vaginal Prevotella species. We previously showed that one such bacteroidetocin, Bd-A, is active at nanomolar concentrations, is water soluble, and is bactericidal, all desirable features in a therapeutic antibacterial peptide. Here, we identify the target of several of the bacteroidetocins as the essential outer membrane protein BamA. Although mutations in bamA can be selected in bacteria grown in vitro, we show both in a mouse model and in human gut ecosystems that bamA mutants leading to Bd-A resistance are fitness attenuated and are not selected. These features further support the potential usefulness of the bacteroidetocins as therapeutics for maladies associated with pathogenic Prevotella species, such as recurrent bacterial vaginosis, for which there are few effective treatments.Funding Information
- HHS | National Institutes of Health (T32AI007061)
- HHS | National Institutes of Health (R01AI132580)
This publication has 30 references indexed in Scilit:
- The Phyre2 web portal for protein modeling, prediction and analysisNature Protocols, 2015
- An antimicrobial protein of the gut symbiont Bacteroides fragilis with a MACPF domain of host immune proteinsMolecular Microbiology, 2014
- Lectin-Like Bacteriocins from Pseudomonas spp. Utilise D-Rhamnose Containing Lipopolysaccharide as a Cellular ReceptorPLoS Pathogens, 2014
- Protease homolog BepA (YfgC) promotes assembly and degradation of β-barrel membrane proteins in Escherichia coliProceedings of the National Academy of Sciences of the United States of America, 2013
- Structural insight into the biogenesis of β-barrel membrane proteinsNature, 2013
- Conformation-specific labeling of BamA and suppressor analysis suggest a cyclic mechanism for β-barrel assembly in Escherichia coliProceedings of the National Academy of Sciences of the United States of America, 2013
- An Extracellular Loop of the Mannose Phosphotransferase System Component IIC Is Responsible for Specific Targeting by Class IIa BacteriocinsJournal of Bacteriology, 2010
- A σ54-dependent PTS permease of the mannose family is responsible for sensitivity of Listeria monocytogenes to mesentericin Y105Microbiology, 2001
- Analysis of σ54-dependent genes in Enterococcus faecalis: a mannose PTS permease (EIIMan) is involved in sensitivity to a bacteriocin, mesentericin Y105Microbiology, 2001
- Absence of a Putative Mannose-Specific Phosphotransferase System Enzyme IIAB Component in a Leucocin A-Resistant Strain of Listeria monocytogenes , as Shown by Two-Dimensional Sodium Dodecyl Sulfate-Polyacrylamide Gel ElectrophoresisApplied and Environmental Microbiology, 2000