High CO2 partial pressure depresses productivity and bioenergetic growth yield of Chlorella pyrenoidosa culture

When low-CO₂ grown Chlorella pyrenoidosa (YSK strain) cells were exposed to high CO₂ partial pressures (pCO₂), the specific growth rate (μ) declined exponentially reaching a steady state value in about 20 h. A short interruption (up to 1 h) by temporarily lowering the pCO₂ did not prevent the continuous decline in μ when high pCO₂ was restored. In chemostate studies, light-limited cultures were supplied with 2 to 90 kPa of CO₂. The steady state biomass production rate and bioenergetic growth yield were related inversely to pCO₂ and the average energy uptake rate. The maintenance energy coefficient was, however, independent of dissolved pCO₂ in the pCO₂ range studied.