Transcriptomic and phenotypic characterization of a Bacillus subtilis strain without extracytoplasmic function σ...

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Genetics

Background:

• Bacillus subtilis possesses seven extracytoplasmic function (ECF) sigma factors, crucial for regulating gene expression in response to environmental cues.
• Three ECF sigma factors (σ(M), σ(W), and σ(X)) are known to mediate responses to cell envelope-active antibiotics.
• The specific functions and regulatory roles of the remaining ECF sigma factors (σ(V), σ(Y), σ(Z), and σ(YlaC)) remain largely undefined.

Purpose of the Study:

• To elucidate the distinct transcriptomic and phenotypic roles of the seven ECF sigma factors in Bacillus subtilis under non-stress conditions.
• To identify novel genes regulated by ECF sigma factors and understand their contribution to cellular processes like biofilm formation.
• To define the specific contributions of individual and combined ECF sigma factors to antibiotic resistance.

Main Methods:

• Comparative transcriptomic analysis of a Bacillus subtilis strain lacking all seven ECF sigma factor genes (Δ7ECF mutant), a triple mutant lacking σ(M), σ(W), and σ(X) (ΔMWX mutant), and the parental 168 strain.
• Phenotypic characterization focusing on biofilm formation and antibiotic sensitivity.
• Identification of genes with differential expression across the mutant strains.

Main Results:

• Over 80 genes were identified as at least partially dependent on ECF sigma factors for their expression.
• The Δ7ECF mutant exhibited significantly reduced expression of genes involved in exopolysaccharide (EPS) production, including the eps operon, leading to impaired biofilm formation.
• While the ΔMWX mutant showed sensitivity to various antibiotics, the Δ7ECF mutant displayed similar or slightly increased sensitivity, highlighting the cumulative role of all ECF sigma factors in resistance.

Conclusions:

• The study underscores the extensive overlap and interconnectedness of the seven ECF sigma factor regulons in Bacillus subtilis.
• σ(M), σ(W), and σ(X) are confirmed as the primary drivers of intrinsic antibiotic resistance in Bacillus subtilis.
• The research provides foundational insights into the previously unknown functions of ECF sigma factors σ(V), σ(Y), σ(Z), and σ(YlaC), particularly their roles in EPS production and biofilm development.