DNA as an Adhesin: Bacillus cereus Requires Extracellular DNA To Form Biofilms

• DOI: 10.1128/aem.01317-08
• Publication Date: 2009-02-28T02:37:41Z
• Authors: Sébastien Vilain; Jakobus M. Pretorius; Jacques Theron; Volker S. Brözel
• Keywords: DNA, Bacterial; 0301 basic medicine; Mutagenesis, Insertional; 03 medical and health sciences; Bacillus cereus; Genes, Bacterial; Biofilms; Gene Expression Profiling; DNA Transposable Elements; Adhesins, Bacterial; Gene Deletion

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 Tn 917 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.