UNIQUE STRATIFICATION OF BIOFILM DENSITY IN MEMBRANE-AERATED BIOFILMS: AN EXPERIMENTAL AND MODELING STUDY

The cell density of biofilms affects volumetric reaction rates, biofilm growth rates, substrate diffusion, yet the mechanisms and dynamics of biofilm density development are poorly understood. In this study, a counter-diffusional membrane-aerated biofilm was used to explore spatial and temporal patterns of density development. After inoculation, the biofilm quickly grew at a low cell density. However, as the biofilm reached a stable thickness of around 1,000 µm, a high cell density layer developed in the biofilm interior. The layer slowly expanded over time. Oxygen microprofiles in the biofilm showed this layer coincided with the metabolically active zone resulting from counter-diffusing O2 and acetate. The formation of this dense layer appeared to be related to changes in growth rates. A mathematical model was also applied to explore the hypothesis of high-cell-density formation. Together, these results suggest that low growth rates can lead to high-density zones within the interior of MAB biofilms.