Bistability in the Bacillus subtilis K-state (competence) system requires a positive feedback loop

Area of Science:

• Microbiology
• Molecular Biology
• Systems Biology

Background:

• High expression of the transcriptional activator ComK is observed in a subset of Bacillus subtilis cells during stationary phase.
• ComK regulates over 100 genes, establishing a unique 'K-state' separate from vegetative growth and sporulation.
• Genes activated by ComK are crucial for establishing competence, enabling genetic transformation.

Purpose of the Study:

• To investigate the regulatory mechanisms underlying the bistability of ComK expression in Bacillus subtilis.
• To determine the role of positive autoregulation and potential toggle switches in ComK expression dynamics.
• To explore the sources of noise contributing to the stochastic activation of ComK.

Main Methods:

• Analysis of ComK expression patterns in Bacillus subtilis strain 168.
• Investigating the role of positive autoregulation at the comK promoter.
• Evaluating the contribution of a ComK-Rok toggle switch mechanism.

Main Results:

• Bistability in ComK expression necessitates positive autoregulation at the comK promoter.
• A potential toggle switch involving ComK and Rok is not required for ComK expression bistability.
• The study identifies factors contributing to the stochastic nature of ComK activation.

Conclusions:

• Positive autoregulation is the key driver of ComK expression bistability in Bacillus subtilis.
• The findings propose a revised model for comK gene regulation, partially explaining the observed bistability.
• Understanding ComK regulation provides insights into the control of genetic competence in bacteria.