Experimental reproducibility in flow-chamber biofilms

The Technical University of The structural organization of microbial commun ities is influenced by many factors, e.g. nutrient composition, shear stres s and temperature. This paper Microbiology, The presents a general method f or quantitative comparison of biofilm structures Technical University of an d assessment of experimental reproducibility between independent biofilm ex periments. By using a novel computer program, COMSTAT, biofilm structures o f Pseudomonas aeruginosa and an isogenic rpoS mutant were quantified. The s trains were tagged with the green fluorescent protein (GFP) and grown in fl ow chambers with a defined minimal medium as substrate. Three independent r ounds of biofilm experiments were performed and in each round, each of the two variants was grown in two separate channels. Nine image stacks were acq uired in each channel 146 h after inoculation. An analysis of variance mode l incorporating the factors experiment round, bacterial strain, channel num ber and image stack number was used to analyse the data calculated by COMST AT. Experimental reproducibility was verified by estimating the magnitude o f the variance of the effects round (sigma (2)(R)) and the interaction betw een bacterial strain and round (sigma (2)(BR)). Mean thickness of the wild- type and rpoS mutant biofilms was estimated at 6.31 mum (SE 0.81 mum) and 1 6.85 mum (SE 0.87 mum), respectively.