Bacillus thuringiensis CbpA is a collagen binding cell surface protein under c-di-GMP control

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Pathogenesis

Background:

• Cyclic diguanylate (c-di-GMP) is a crucial second messenger regulating cellular processes in Bacillus cereus group bacteria, including biofilm formation and motility.
• CdgF, a diguanylate cyclase, promotes biofilm formation in B. thuringiensis, and a c-di-GMP-responsive riboswitch upstream of cbpA is conserved in B. cereus group strains.
• CbpA was predicted as a cell wall-anchored surface protein with potential fibrinogen or collagen binding domains.

Purpose of the Study:

• To identify the binding ligand of CbpA.
• To elucidate the function of CbpA within the Bacillus cereus group c-di-GMP regulatory network.

Main Methods:

• Global gene expression profiling to analyze cbpA regulation in a cdgF deletion mutant.
• Cell adhesion assays to determine CbpA binding to collagen, fibrinogen, and fibronectin.
• Assessment of CbpA's contribution to binding abiotic surfaces and its effect on motility and biofilm formation.

Main Results:

• cbpA expression was downregulated in a cdgF deletion mutant and peaked during early exponential growth.
• A ΔcbpA deletion mutant showed no collagen binding, while CbpA overexpression increased collagen binding.
• CbpA did not affect binding to fibrinogen, fibronectin, or abiotic surfaces; however, CbpA overexpression reduced motility and biofilm formation.

Conclusions:

• This study provides the first experimental evidence that collagen is the binding ligand for the c-di-GMP regulated adhesin CbpA.
• CbpA plays a role in collagen binding and influences motility and biofilm formation in Bacillus cereus group bacteria.