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Cellular material and extracellular polymeric substances are the
basic structural elements in biofilm systems. The structure and role
of EPS for biofilm development and metabolic processes have not been
precisely determined and, therefore, have not yet been included as a
necessary element in modelling and simulation studies. This is due
to the difficulty of experimentally detecting the extracellular
polymeric substances in situ and differentiating them from cellular
material on the one hand, and to the subsequent uncertainty about
appropriate models--e.g. rigid hindrances, porous microstructure or
visco-elastic structure--on the other hand. In this work, we report
on the use of confocal laser scanning microscopy to monitor the
development of a monoculture biofilm of Sphingomonas sp. grown in a
flow cell. The bacterial strain was genetically labelled resulting
in strong constitutive expression of the green fluorescent protein.
The development of extracellular polymeric substances was followed
by binding of the lectin concavalin A to cell exopolysaccharides.
The growth of the resulting strain was digitally recorded by
automated confocal laser scanning microscopy. In addition, local
velocity profiles of fluorescent carboxylate-modified microspheres
were observed on pathlines throughout the biofilm. The CLSM image
stacks were used as direct input for the explicit modelling and
three-dimensional numerical simulation of flow fields and solute
transport processes based on the conservation laws of continuum
mechanics. At present, a strongly simplifying EPS-model is applied
for numerical simulations. The EPSs are preliminarily assumed to
behave like a rigid and dense hindrance with diffusive-reactive
solute transport.
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