ABC Transporter DerAB of Lactobacillus casei Mediates Resistance against Insect-Derived Defensins

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Bce-like systems are crucial for antimicrobial peptide (AMP) resistance in Firmicutes bacteria.
• An orphan ABC transporter in Lactobacillus casei BL23 was previously hypothesized to mediate AMP resistance.

Purpose of the Study:

• To characterize the function of the orphan ABC transporter in Lactobacillus casei BL23.
• To investigate its role in antimicrobial peptide resistance and its interaction with other resistance systems.

Main Methods:

• Construction and sensitivity testing of a mutant lacking the permease subunit of the orphan transporter.
• Evaluation of resistance against a diverse panel of antimicrobial peptides.
• Analysis of gene expression changes in response to transporter absence.
• Bacterial two-hybrid assays to study protein interactions.

Main Results:

• The transporter, renamed DerAB (defensin resistance ABC transporter), specifically confers resistance against insect-derived defensins.
• Absence of DerAB leads to increased resistance against the lantibiotic nisin.
• This heightened nisin resistance is due to upregulated expression of PsdRSAB and ApsRSAB determinants.
• DerB interacts with the Psd resistance system, suggesting signaling interference.

Conclusions:

• DerAB is a novel ABC transporter crucial for resistance against insect defensins, representing an interkingdom defense mechanism.
• DerAB negatively interferes with the PsdRSAB system, modulating nisin resistance.
• The Lactobacillus casei BL23 Bce modules demonstrate a paradox where maximal nisin resistance occurs without the defensin-specific transporter.