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 3.3 mM, and a light intensity of ~ 202 μE m− 2 s− 1. Among the pH values tested, pH 8.5 supported the highest maximum specific growth rate (μmax), 2.4/day that was statistically larger than μmax values at pH 7.5 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: 86 μM for pH 8.5, 84 μM for pH 7.5, and 96 μM for pH 9.5, values that were statistically indistinguishable. All KCib values were small, indicating that Synechocystis has a high affinity for Cib, attaining μmax by ~ 1 mM. Analyzing the kinetics individually for each Ci species supports that bicarbonate best represented the rate of Ci uptake.

Original languageEnglish (US)
Pages (from-to)363-369
Number of pages7
JournalAlgal Research
StatePublished - Nov 1 2016


  • Cyanobacteria
  • Growth kinetics
  • Inorganic carbon
  • Synechocystis
  • pH

ASJC Scopus subject areas

  • Agronomy and Crop Science


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