Phosphate and Silicate Kinetics for the Lake Michigan Diatom Diatoma Elongatum

Growth rates and uptake rates by a clone of Diatoma elongatum isolated from Lake Michigan were measured under silicate and phosphate limitation using batch and semicontinuous methods. Under phosphate limited batch growth conditions, the half saturation constant for growth (K) was 0.02 μM PO₄-P and the maximum growth rate (μ_m) was 0.7 doublings day^-1; under silicate limited conditions, K was 1.51 μM SiO₂-Si, and μ_m was 1.2 doublings day^-1. The results from these direct measurements of growth under nutrient limitation agreed well with the steady state kinetic information obtained for a two-step (uptake and utilization) growth model Batch uptake experiments and steady state growth experiments provided kinetic information used to estimate K, the calculated half saturation constant for growth. K was 0.03 μM PO₄-P under phosphate limitation, and 1.18 μM SiO₂-Si under silicate limitation. We observed a dependence of the coefficient of luxury consumption on the steady state growth rate. D. elongatum can have up to 28 times more phosphate stores than needed, and up to 4.4 times more silicate.