TABLE 2.

Differences between 4- and 7-day biofilm structural parameters

Structural parametera	Value forb:
	4-day biofilm	7-day biofilm
Biovolume (log μm3)	7.31 ± 0.06*	7.58 ± 0.03*
Biofilm thickness (μm)	39.50 ± 5.60*	86.0 ± 2.50*
Biomass thickness (μm)	46.3 ± 2.90*	88.2 ± 3.20*
Biovolume-to-surface area ratio	1.7 ± 0.07	1.9 ± 0.08
Porosity	0.71 ± 0.06	0.61 ± 0.05
Diffusion distance (μm)	3.44 ± 0.37*	5.14 ± 0.31*

^aBiovolume is the total volume of the biofilm biomass. Biofilm thickness is the volume of the biofilm divided by the total surface area imaged. Biomass thickness is the volume of the biofilm divided by only that area of the substratum covered by the cells. Porosity is the ratio of total void volume to total biofilm volume. Diffusion distance is the average diffusion distance across all cell clusters in the biofilm.

^bValues are means ± standard errors from 4 independent experiments. Values that differ significantly (P < 0.05) between 4- and 7-day biofilms are indicated with an asterisk. Comparisons were made using a t test (significance is based on the Bonferroni adjustment; P < 0.008).