Phosphatase activities of cultured phototrophic biofilms

The responses of cultured phototrophic biofilms to diverse phosphorus (P) regimes were assessed using a semi-continuous flow incubator. Three biofilms were grown over 18 days under three different P regimes: replete inorganic P, organic P-only and limited inorganic P. Assessing the response of the biofilms took into account the rate of phosphomonoesterase and phosphodiesterase activities, biofilm nutrient contents and biomass accrual across the growth period. Phosphorus limitation was indicated by slower biomass accumulation and higher phosphatase activities of the organic P-only and P-limited biofilms compared to the P-replete biofilms. The cyanobacterium Phormidium sp. dominated the later stages in all the treatments forming a dense layer at the biofilm-medium interface. This layer possibly led to a reduction of light and nutrient diffusion to sub-surface cells and may account for the production of phosphatases under P replete conditions. In addition, the Phormidium-layer possibly produced a top-heavy P (and N) distribution and could explain the large reductions in areal nutrient concentrations. End-product repression and de-repression of phosphatase activity was suggested to be a main controlling factor of phosphatase activity. Consequently, it is proposed that for efficient nutrient removal from wastewaters that biofilms should be regularly removed to continually maintain biofilms at the initial stages (3-7 days).