Abstract
Growth pH and the concentration of bioavailable inorganic carbon (Cib) are two essential factors controlling the rate of photoautotrophic growth of microalgae. We developed a novel experimental strategy to determine the effects of pH and Cib independently by a pH-Stat and the use of NH4NO3 as the N source. We grew Synechocystis sp. PCC 6803 at pH values of 7.5, 8.5, and 9.5, with a stable inorganic carbon (Ci) concentration ranging from 0.08 to 3.3mM, and a light intensity of ~202μEm−2s−1. Among the pH values tested, pH8.5 supported the highest maximum specific growth rate (μmax), 2.4/day that was statistically larger than μmax values at pH7.5 and 9.5, about 2.0/day. Using the sum of dissolved CO2, carbonic acid, and bicarbonate (i.e., Cib) to fit Monod kinetics, we found the half-maximum-rate concentrations (KCib) were in a narrow range: 86μM for pH8.5, 84μM for pH7.5, and 96μM for pH9.5, values that were statistically indistinguishable. All KCib values were small, indicating that Synechocystis has a high affinity for Cib, attaining μmax by ~1mM. Analyzing the kinetics individually for each Ci species supports that bicarbonate best represented the rate of Ci uptake.
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