Measurement of local diffusion coefficients in biofilms by microinjection and confocal microscopy.

A new technique for the determination of local diffusion coefficients in biofilms is described. It is based on the microinjection of fluorescent dyes and quantitative analysis of the subsequent plume formation using confocal laser microscopy. The diffusion coefficients of fluorescein (MW 332), TRITC-IgG (MW 150000) and phycoerythrin (MW 240000) were measured in the cell clusters and interstitial voids of a heterogeneous biofilm.

Effect of low-intensity ultrasound upon biofilm structure from confocal scanning laser microscopy observation.

Ultrasonic irradiation at 500 kHz and 10 mW cm-2 of a 24 h old biofilm of P. aeruginosa enhanced the killing of bacteria by gentamicin. To determine whether this bioacoustic effect was caused by ultrasonic-induced changes in the biofilm morphology (biofilm breakup or disruption), the biofilms were examined by confocal scanning laser microscopy (CSLM).

Liquid flow in heterogeneous biofilms.

Liquid flow was studied in aerobic biofilms, consisting of microbial cell clusters (discrete aggregates of densely packed cells) and interstitial voids. Fluorescein microinjection was used as a qualitative technique to determine the presence of flow in cell clusters and voids. Flow velocity profiles were determined by tracking fluorescent latex spheres using confocal microscopy.

Liquid flow in biofilm systems.

A model biofilm consisting of Pseudomonas aeruginosa, Pseudomonas fluorescens, and Klebsiella pneumoniae was developed to study the relationships between structural heterogeneity and hydrodynamics. Local fluid velocity in the biofilm system was measured by a noninvasive method of particle image velocimetry, using confocal scanning laser microscopy. Velocity profiles were measured in conduit and porous medium reactors in the presence and absence of biofilm.

Effects of biofilm structures on oxygen distribution and mass transport.

Aerobic biofilms were found to have a complex structure consisting of microbial cell clusters (discrete aggregates of densely packed cells) and interstitial voids. The oxygen distribution was strongly correlated with these strutures. The voids facilitated oxygen transport from the bulk liquid through the biofilm, supplying approximately 50% of the total oxygen consumed by the cells.