Influence of Flow Velocity on the Characteristics of Pseudomonas fluorescens Biofilms

The characteristics of Pseudomonas fluorescens biofilms formed under three different linear flow velocities (u=0.1, 0.4, and 0.8m/s; Reynolds numbers of 1,000, 4,000, and 8,000, respectively) were studied providing an extension to the studies of earlier researchers. A flow cell reactor system was used to form biofilms, and they were characterized in terms of thickness, morphological structure, mass, cell density, outer membrane protein expression, and matrix and total protein and polysaccharide content. The external mass transfer coefficients were also assessed. The biofilms developed at u=0.4 and 0.8m/s had similar characteristics but were significantly different from those developed at 0.1m/s. High flow velocities formed thinner biofilms with higher cell densities and contents of matrix/extracellular proteins and polysaccharides. The increase of flow velocity from 0.4 to 0.8m/s caused a higher production of matrix proteins and polysaccharides. The external mass transfer coefficients suggest mass transfer limitations for the lowest velocity. Scanning electron microscopy images show cell-surface and cell-cell attachment structures appearing more frequently in biofilms formed at the two higher velocities. No major differences were found in the outer membrane protein expression of biofilm cells formed under the selected linear flow velocities. The overall results show the effect of the hydrodynamic conditions under which biofilms were formed on selected macromolecular characteristics, demonstrating that higher flow velocities can originate more complex and denser biofilms.