Effects of inorganic carbon and pH on growth kinetics of Synechocystis sp PCC 6803

Growth pH and the concentration of bioavailable inorganic carbon (C-ib) 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 C-ib 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 (C-i) concentration ranging from 0.08 to 3.3 mM, and a light intensity of similar to 202 mu E m(-2) s(-1). Among the pH values tested, pH 8.5 supported the highest maximum specific growth rate (mu(max)), 2.4/day that was statistically larger than mu(max) values at pH 7.5 and 9.5, about 2.0/day. Using the sum of dissolved CO2, carbonic acid, and bicarbonate (i.e., C-ib) to fit Monod kinetics, we found the half-maximum-rate concentrations (KCib) were in a narrow range: 86 mu M for pH 8.5, 84 mu M for pH 7.5, and 96 mu M for pH 9.5, values that were statistically indistinguishable. All KCib values were small, indicating that Synechocystis has a high affinity for C-ib, attaining mu(max) by similar to 1 mM. Analyzing the kinetics individually for each Ci species supports that bicarbonate best represented the rate of Ci uptake. (C) 2016 Elsevier B.V. All rights reserved.