Effects of photosynthesis on bacterial phosphatase production in biofilms

The fraction of bacteria displaying phosphatase activity within natural pho tosynthetic biofilms was examined in relation to phosphorus limitation and algal photosynthesis. An artificial substrate that forms a fluorescent prec ipitate was used in conjunction with the nucleic acid stain DAPI to enumera te extracellular phosphatase expression by biofilm bacteria exposed to diff erent photosynthetic activities and phosphorus supplies. The proportion of bacteria displaying phosphatase activity changed in response to the presenc e or absence of algal photosynthesis. in general, phosphate-deprived biofil ms had positive linear trends in bacterial phosphatase activity (p < 0.001) , with greater proportions of bacteria displaying phosphatase under photosy nthetic inhibition compared to active photosynthesis. Under sufficient phos phate supplies, biofilms had negative linear trends (p < 0.05) or were lowe r in the proportion of bacteria displaying phosphatase activity in the pres ence of algal photosynthesis, whereas bacterial phosphatase activity was ge nerally maintained when photosynthesis was inhibited. It is suggested that the amount of extracellular organic carbon released within the biofilm matr ix during photosynthesis indirectly affected bacterial phosphatase synthesi s.