Correlation of extracellular polymeric substances and microbial communities in biofilms with phosphate

Abstract The characteristics and dynamic succession of biofilm on the surface of attached materials at different phosphate levels were studied. Phosphate showed significant effect on the formation of biofilm. The dry weight, dry weight without ash, chlorophyll-a, and extracellular polymeric substances (EPS) of biofilm all increased with the increase of phosphate level, and reached the peak value at 40 µg/L, then stabilized and slightly decreased with the increase of phosphate concentration. The proportion of polysaccharides in EPS of each layer in biofilm increased from outside to inside (from Soluble EPS to Loosely Bound EPS to Tightly Bound EPS), in contrast, the proportion of protein showed the opposite. EPS of various types in biofilms enhanced with the increase of phosphate level, the amounts of protein and polysaccharide in EPS showed similar trend. When the phosphate concentrations were lower than 40 µg/L, the ratio of protein to polysaccharide (PN/PS) increased with the increase of phosphate level, and decreased somewhat when the phosphate was higher than 50 µg/L. The proportion of bacteria in microbial population of biofilm decreased with the increasing of phosphate level and immersion time of the attached material, while the proportion of diatoms increased gradually. The study was helpful to understand the dialectical relationship between environmental factors and biological factors in the aquaculture environment, and provides a theoretical basis for exploring the mechanism of marine biofilm formation.