PREDICTING THE KINETICS OF DISSOLVED INORGANIC CARBON LIMITED GROWTH FROM THE SHORT-TERM KINETICS OF PHOTOSYNTHESIS IN SYNECHOCOCCUS LEOPOLIENSIS (CYANOPHYTA)1

The blue-green alga (Cyanobacterium) Synechococcus leopoliensis (Racib.) Komarek was grown in dissolved inorganic carbon [DIC]-limited chemostats over the entire range of growth rates. At each growth rate, the kinetics of photosynthesis with respect to [DIC] and the maximal rate of photosynthesis (Pmax) were determined. The half-saturation constant for [DIC]-limited photosynthesis (K1/2DIC) for cells growing below 1.7 d−1 was constant (4.7 μM) whereas for growth rates between 1.7 d−1 and 2.1 d−1 (μmax) the kinetics of photosynthesis were multiphasic with an apparent K1/2DIC between 1.5–2.0 mM. Pmax increased in a linear fashion with growth rate for growth rates below 1.7 d−1. No trend in Pmax was apparent for growth rates greater than 1.7 d−1. These kinetic parameters were used to predict a growth rate versus [DIC] relationship. Results show that the Monod relationship is a physiologically valid expression of growth as a function of [DIC] provided (K1/2DIC) remains constant. The major change in (K1/2DIC) as μ approaches μmax results in the conclusion that two separate and distinct Monod equations must be used to describe growth as a function of DIC over the entire growth range. These results point to a major discontinuity in the μ vs. [DIC] curve at 1.7 d−1 which corresponds to the change from high to low affinity photosynthetic kinetics. We believe these results account for the previously described deficiencies of the Monod equation in describing [DIC]-limited algal growth.