Method for determining the temporal response of microbial phosphate transport affinity.

Nutrient transport affinities of nutrient-starved microbial populations were measured as initial slopes of plots of limiting-nutrient transport rates versus extracellular limiting-nutrient concentrations. A method was devised for the determination of soluble reactive phosphate (Pi) affinity in Pi-limited continuous culture (aT), which was then used as an indicator of the effects of light/dark cycle (LD) perturbations on the temporal Pi transport abilities of three species of freshwater algae. Cell division was asynchronous for the green alga Selenastrum capricornutum grown in continuous cultures exposed to LD cycles. An apparent rhythm in aT for Pi was greatly affected by the population size parameter. Cell division was phased for the green alga Scenedesmus quadricauda grown in LD continuous culture. A rhythm in aT for Pi was not greatly affected by the biomass parameter. Cell division was also phased in LD continuous culture for the blue-green alga (cyanobacterium) Synechococcus Nägeli, but rhythms in other parameters could not be detected. Synechococcus Nägeli was an extremely efficient Pi transporter at low Pi concentrations in LD continuous culture, and so aT could not be calculated. The results demonstrate that aT is well suited to describing the temporal response of Pi transport in LD-perturbed, Pi-limited continuous culture.