Adaptor-mediated Lon proteolysis restricts Bacillus subtilis hyperflagellation

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• The Lon AAA+ protease is a conserved intracellular protease involved in protein quality control and virulence regulation.
• Its mechanism for discriminating between numerous protein targets is not fully understood.
• Lon proteases are targets for anticancer therapies in eukaryotes and virulence control in bacteria.

Purpose of the Study:

• To investigate the specific targets and regulatory mechanisms of the Bacillus subtilis LonA protease.
• To elucidate how LonA activity is regulated in response to environmental cues, specifically surface contact.
• To understand the role of LonA in bacterial motility and cellular differentiation.

Main Methods:

• Proteolysis assays using purified Bacillus subtilis LonA and its substrates.
• Genetic manipulation of Bacillus subtilis strains to study the roles of LonA, SwrA, and SmiA.
• Microscopy techniques to analyze flagellar expression and bacterial swarming behavior on solid surfaces.

Main Results:

• Bacillus subtilis LonA specifically degrades the master regulator of flagellar biosynthesis, SwrA, in a process mediated by the adaptor protein SmiA.
• Proteolysis of SwrA by LonA is inhibited upon bacterial contact with a surface.
• Cessation of SwrA degradation leads to increased SwrA protein levels and enhanced flagellar density, triggering swarming motility.

Conclusions:

• Regulated proteolysis by LonA, modulated by adaptor proteins like SmiA, is a key mechanism controlling bacterial adaptation to surface environments.
• Surface contact acts as a signal to rapidly alter protein degradation pathways, influencing bacterial behavior and differentiation.
• This study reveals a novel mechanism for transducing surface stimuli through regulated proteolysis, with implications for understanding bacterial virulence and multicellular behaviors.