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

Abstract

Cyclic diguanylate (c-di-GMP) signalling affects several cellular processes in Bacillus cereus group bacteria including biofilm formation and motility, and CdgF was previously identified as a diguanylate cyclase promoting biofilm formation in B. thuringiensis. C-di-GMP can exert its function as a second messenger via riboswitch binding, and a functional c-di-GMP-responsive riboswitch has been found upstream of cbpA in various B. cereus group strains. Protein signature recognition predicted CbpA to be a cell wall-anchored surface protein with a fibrinogen or collagen binding domain. The aim of this study was to identify the binding ligand of CbpA and the function of CbpA in cellular processes that are part of the B. cereus group c-di-GMP regulatory network. By global gene expression profiling cbpA was found to be down-regulated in a cdgF deletion mutant, and cbpA exhibited maximum expression in early exponential growth. Contrary to the wild type, a ΔcbpA deletion mutant showed no binding to collagen in a cell adhesion assay, while a CbpA overexpression strain exhibited slightly increased collagen binding compared to the control. For both fibrinogen and fibronectin there was however no change in binding activity compared to controls, and CbpA did not appear to contribute to binding to abiotic surfaces (polystyrene, glass, steel). Also, the CbpA overexpression strain appeared to be less motile and showed a decrease in biofilm formation compared to the control. This study provides the first experimental proof that the binding ligand of the c-di-GMP regulated adhesin CbpA is collagen.

MogR is a ubiquitous transcriptional repressor affecting motility, biofilm formation and virulence inBacillus thuringiensis

“…Genes in this locus have been found to be implicated in biofilm formation in B. cereus in a pellicle biofilm model (Hayrapetyan et al, 2015; Okshevsky et al, 2017). Another upregulated gene was cbpA , encoding a collagen adhesion protein positively regulated by c-di-GMP (Finke et al, 2019).…”

Characterization of the dual regulation by a c-di-GMP riboswitch Bc1 with a long expression platform from Bacillus thuringiensis

“…In some cases, dual terminators are more effective than single terminators in transcription repression ( 78 – 80 ). c-di-GMP riboswitches generally control transcription by forming a single ρ-(in)dependent terminator ( 77 , 81 ), and some do not even contain any terminator ( 31 , 37 – 39 , 68 ). A riboswitch containing a dual terminator within a single EP is rarely seen in previous studies.…”

Tandem Mass Tag-Based Quantitative Proteomics and Virulence Phenotype of Hemolymph-Treated Bacillus thuringiensis kurstaki Cells Reveal New Insights on Bacterial Pathogenesis in Insects

“…Changes in biofilm formation due to hemolymph exposure were assayed by the ability of Bt cells to adhere to the wells of 24-well polystyrene plates ( 98 ). LB medium was preequilibrated for 16 h at 30°C in 24-well polystyrene plates (Falcon) before inoculation with 1:10 dilutions of 60-min static Btk-T or Btk cultures.…”