Biofilm growth and internal structures were investigated by Confocal Scanning Laser Microscopy and fluorescently labeled oligonucleotide probe hybridization. Biofilms on smooth flat surfaces such as glass slides grew as isolated cell clusters. Under a hydraulic linear flow velocity of 1.7 cm/s mature biofilms exhibited a network like structure consisting of large interconnected cell clusters leading to possible three-dimensional mass transport. Smooth curved tube surfaces were also colonized by isolated cell clusters. However a clustered structure was not observed in mature tubular biofilms which grew as a continuum. Under laminar flow conditions, the tubular biofilms had a uniform cell distribution along the depth with a flat surface profile. The dense tubular biofilms produced under turbulent flow had a stratified structure with thickness. Morphologically these had an irregular surface profile with protrusions extending from a thick base layer. The production of extracellular polymeric substances were both cell physiology and growth related. While hydrodynamic condition was shown to be an effective tool for manipulation of biofilm structures, the relationship of the structure to biological activity and process control needs further investigation.

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