LanI-Mediated Lantibiotic Immunity in Bacillus subtilis: Functional Analysis

Area of Science:

• Microbiology and Molecular Biology
• Antimicrobial Peptides
• Bacterial Immunity Mechanisms

Background:

• Lantibiotics subtilin and nisin, produced by *Bacillus subtilis* and *Lactococcus lactis*, possess antimicrobial activity.
• Producing bacteria require immunity mechanisms, including immunity proteins (SpaI, NisI) and ABC transporters (SpaFEG, NisFEG), to prevent self-toxicity.
• The precise molecular function and physiological role of lantibiotic immunity lipoproteins remain largely unelucidated.

Purpose of the Study:

• To investigate the molecular interaction between subtilin and its cognate immunity lipoprotein, SpaI.
• To determine the physiological function of SpaI in protecting *Bacillus subtilis* from subtilin-induced toxicity.
• To elucidate the structural requirements of subtilin for interaction with SpaI.

Main Methods:

• Laser-induced liquid bead ion desorption (LILBID)-mass spectrometry was employed to detect subtilin-SpaI interactions.
• Functional assays were conducted in *B. subtilis* strains expressing SpaI or NisI to assess resistance against subtilin and nisin.
• Pore formation assays were used to evaluate the protective efficacy of SpaI and SpaFEG against lantibiotic action.
• A nisin-subtilin hybrid molecule was utilized to identify key regions of subtilin involved in SpaI-mediated immunity.

Main Results:

• Lantibiotics subtilin and nisin interact specifically with their cognate immunity lipoproteins, SpaI and NisI, respectively.
• Expression of SpaI or NisI confers resistance to subtilin or nisin in non-producing strains by preventing pore formation.
• The C-terminal region of subtilin, but not its lanthionine rings, is crucial for SpaI-mediated immunity.
• SpaI provides efficient pore formation prevention, acting as a rapid membrane protection mechanism, though less effective in growth protection than the SpaFEG transporter.

Conclusions:

• SpaI functions as a critical component of the bacterial immune system, offering rapid protection against lantibiotic toxicity.
• The interaction between subtilin and SpaI is mediated by the C-terminal portion of the lantibiotic.
• Understanding lantibiotic immunity mechanisms is vital for enhancing antimicrobial peptide production and engineering novel antibiotics.