Bacterial utilization of algal extracellular products. 2. A kinetic study of natural populations

The uptake of 14 C‐labeled extracellular products from Skeletonema costatum by native bacterial populations was analyzed during a bloom of this alga in the Trondheimsfjord, Norway. Data in agreement with the linear predictions of a mixed‐substrate kinetic model were obtained on each of 10 separate occasions. Changes in the kinetic parameters indicated that a 4‐fold increase in bacterial activity was enough to prevent a large accumulation of dissolved extracellular products. Transient inhibition of bacterial activity occurred during the late exponential phase of the algal bloom. Labeled extracellular products from Chaetoceros affinis were not utilized in a manner that could be analyzed according to the kinetic model. The data indicate that the bloom of S. costatum stimulated the activity of a specific bacterial flora which established a dynamic equilibrium between the release and consumption in situ of extracellular products.