Algal Excretion of 14c‐labeled Compounds and Microbial Interactions in Cyanidium Caldarium Mats1

SUMMARY Acid spring effluents are often covered with mats of the eucaryotic phycocyanin‐containing alga. Cyanidium caldarium. The primary bacterial component of such mats is an acidophilic strain of Bacillus coagulans, and the primary fungal component is Dactylaria gallopava. Because of the limited species diversity, C. caldarium mats appeared to be an excellent system for studying algal excretion and various microbial interactions in nature. From 2 to 6% of the NaH14CO3 taken up by natural or laboratory populations of the alga was excreted as 14C‐labeled materials. The maximum excretion occurred at temperature, light, and pH values optimum for NaH14CO3 uptake. However, when excretion was expressed as a percentage of NaH14CO3 uptake, a higher percentage of the radioactivity was excreted at nonoptimal conditions for NaH14CO3 uptake. Fungal biomass was directly proportional to algal density, but bacterial numbers varied widely and did not correlate with algal numbers. The bacterial and fungal components could be grown in mixed culture with either growing C. caldarium cultures or in an extract prepared, by healing algal cells.