Photosynthetic production of biomass and starch by Chlorella in chemostat culture

A high temperature strain of Chlorella was grown photosynthetically with nitrogen limitation of growth over a range of dilution rates up to the critical value of 0.22 h^?1. The “total cell dry weight” is distinguished from the “real biomass” which is total cell dry weight less starch. Nitrogen-limited growth of Chlorella, in terms of real biomass, obeyed the simple Monod model of chemostat culture. In a low EDTA medium (about 1 mol of EDTA per mol Fe³⁺) ferric hydroxide precipitated at pH 7 and caused iron-limited growth to occur at high dilution rates. Iron precipitation and consequently iron-limited growth, were prevented by increasing the EDTA to 2 mol per mol Fe³⁺. It was deduced that Fe³⁺ was available to the cells only as Fe-EDTA complex, not as free Fe³⁺ in the medium. A glycogen-like starch was stored in the cells and the starch content approached 50% of the total dry weight of cells at low dilution rates. The starch content of the total cell dry weight was practically independent of the growth temperature over the range 28–40°C and the pH over the range 5.5–8.5. The specific rate of starch production (q_starch) reached 0.05 g of starch/g real biomass h.