Fig. 2. Expression dynamics of external elements and extracellular-matrix components during biofilm formation.

a Expression dynamics of external elements and extracellular-matrix components during biofilm formation. Comparison of heat maps from RNA-seq (left) and iTRAQ (right) results at 24, 48, and 72 h, over a selection of elements of the outer layers of B. cereus cells and components of the extracellular matrix shows the following: (i) The low expression levels of S-layer components, the major relevance of eDNA at 24–48 h, and the continuous overexpression of factors related to cell wall synthesis, some exopolysaccharides and other adhesins. b Gene clusters for the synthesis of two hypothetical exopolysaccharides: top, eps1, homologous to the eps region in B. subtilis and bottom, eps2 specific of B. cereus. Crystal violet staining of adhered biofilms showed no differences between eps1 single mutant and wild-type, and slight reduction of biofilm formation of eps2 single mutant. The strain eps2 complemented with a replicative plasmid (pUTE973) harboring the transcriptional construction P_IPTG-eps2 showed a reversion on the crystal violet staining. Pictures were taken 72 h after growing cells with no agitation at 28 °C in TY. The adhesion to abiotic surface of the different strains in TyJ medium at 48 h was measured by the amount of crystal violet retained in the bacterial biomass. (error bars correspond to SD.*, differences statistically significant, p < 0.05, T-student, three replicates).