Biofilm formation in a freshwater environment under photic and aphotic conditions

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Abstract
Time series studies have been carried out to characterise biofilms developed on inert surfaces, in naturally lit (photic) as well as dark (aphotic) environments in a freshwater system. Various physical, chemical and biological parameters were studied at 24 h intervals up to 120 h. The results showed a major influence of light on many of the biofilm parameters studied. Biofilm thickness and volume increased from 52 to 128 μm and from 1.03 to 2.57 cc 100cm‐2, respectively, in the photic environment during the period of exposure. In the aphotic biofilm, the thickness and volume ranged from 17 to 30μm and from 0.35 to 0.60cc 100cm‐2. Particle size distribution also showed significant variation; in the aphotic biofilm, the distribution was skewed towards lower particle sizes. Biofilm biomass, chlorophyll a and other constituents were higher under illuminated conditions. Diatom counts were higher on the photic panels. Slime formers constituted 60% of the culturable bacterial population in the biofilm. Protozoan grazing of biofilm bacteria was observed after 72 h in both sets. Nutrients were found to be enriched in the biofilms compared with the ambient water, and concentration factors were consistently higher in the aphotic biofilms than in those grown under photic conditions.