Mutations in ompR and rcsB abolished temporal differences in flhD expression The fluorescence signals from flhD::gfp in the ompR and rcsB mutant strains were higher than those
from the other strains at all times. Expression of flhD in the ompR mutant increased over buy PU-H71 the first 12 h and reached a steady state level after that (Figure 2A, red line, blue squares). Between 12 h and 24 h, expression of flhD in the rcsB mutant (Figure 2A, orange line, blue triangles) increased more slowly than in the ompR mutant, but was reasonably growth phase independent after 24 h as well. This slower increase in flhD expression in the rcsB mutant (relative to the ompR mutant) correlates with the reduced increase in rcsB expression (blue line) during the same time period, relative to the increase in ompR expression (black line). Statistical analysis of the data with the Loess procedure yielded confidence bands for the ompR and rcsB mutant strains that did not overlap with that of the parent (Figure 2B).This indicates that there is indeed a statistically significant difference between the parent strain and either of the two mutants. In comparison, the expression profile for our housekeeping strain that contains
the aceK::gfp fusion plasmid was high at all times (Figure 2A, purple line, cross symbols). Expression increases in any strain during the first 12 h can be explained by the increase in bacterial cell
numbers during the early development of the biofilm. Spatial gene expression of flhD in E. coli biofilm From the temporal gene expression experiment, we knew that VX-680 the highest expression of flhD was at 12 h and 51 h of biofilm formation. As a consequence, we performed the spatial gene expression experiment for flhD at those two time points. In both the 12 h (Figure 3A) and 51 h (Figure 3B) biofilms, the expression of flhD was highest at the outer layer of the biofilm. Fluorescence calculated from the individual images of the z-stacks showed that at 12 h, there was little or no expression of flhD within the first 2 μm from the surface that the biofilm had formed on (dotted yellow lines). check Expression increased rapidly at 2 μm to NSC23766 datasheet approximately 50% coverage. In 51 h biofilms, there were three distinct intensity levels (solid yellow lines). Until 3 μm, the expression of flhD was very low; at 3.5 μm, the expression jumped to 50% and maintained this level until 6 μm; across the upper 2 μm of our biofilm, flhD expression increased to approximately 75% of the total area of the images. Our housekeeping gene in comparison was highly expressed all throughout the biofilm (purple lines). Figure 3 Spatial gene expression of flhD in the parent strain. (A) and (B) are the 3D images constructed from the z-stacked images (bright field and fluorescence) at 12 hours (A) and 51 hours (B), using BP1470 (AJW678 pPS71).