title: DNA as an adhesin: Bacillus cereus requires extracellular DNA to form biofilms.
abstract: The soil saprophyte Bacillus cereus forms biofilms at solid-liquid interfaces. The composition of the extracellular polymeric matrix is not known, but biofilms of other bacteria are encased in polysaccharides, protein, and also extracellular DNA (eDNA). A Tn917 screen for strains impaired in biofilm formation at a solid-liquid interface yielded several mutants. Three mutants deficient in the purine biosynthesis genes purA, purC, and purL were biofilm impaired, but they grew planktonically like the wild type in Luria-Bertani broth. Biofilm populations had higher purA, purC, and purL transcript ratios than planktonic cultures, as measured by real-time PCR. Laser scanning confocal microscopy (LSCM) of BacLight-stained samples indicated that there were nucleic acids in the cell-associated matrix. This eDNA could be mobilized off the biofilm into an agarose gel matrix through electrophoresis, and it was a substrate for DNase. Glass surfaces exposed to exponentially growing populations acquired a DNA-containing conditioning film, as indicated by LSCM. Planktonic exponential-phase cells released DNA into an agarose gel matrix through electrophoresis, while stationary-phase populations did not do this. DNase treatment of planktonic exponential-phase populations rendered cells more susceptible than control populations to the DNA-interacting antibiotic actinomycin D. Exponential-phase purA cells did not contain detectable eDNA, nor did they convey a DNA-containing conditioning film to the glass surface. These results indicate that exponential-phase cells of B. cereus ATCC 14579 are decorated with eDNA and that biofilm formation requires DNA as part of the extracellular polymeric matrix.
authors.affiliation: Department of Biology and Microbiology, South Dakota State University, Brookings, SD 57007, USA.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Vilain
authors.forename: Jakobus M
authors.initials: JM
authors.lastname: Pretorius
authors.forename: Jacques
authors.initials: J
authors.lastname: Theron
authors.forename: Volker S
authors.initials: VS
authors.lastname: Brözel
mesh_terms: D018829:Adhesins, Bacterial / Q000378:metabolism*; D001409:Bacillus cereus / Q000235:genetics / Q000502:physiology*; D018441:Biofilms / Q000254:growth & development*; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000378:metabolism*; D017353:Gene Deletion; D020869:Gene Expression Profiling; D005798:Genes, Bacterial; D016254:Mutagenesis, Insertional
chemical_list: D018829:Adhesins, Bacterial; D004251:DNA Transposable Elements; D004269:DNA, Bacterial