Kinetic analysis of the growth of Chlorella vulgaris

Abstract

The energy of the total transmitted light was subtracted from that of the incident light in a culture vessel and the difference was divided by the weight of cells. The value thus obtained was defined as the amount, E(x), of light energy absorbed per unit cell weight per unit time.Batch and continuous cultures of Chlorella vulgaris were carried out at 30 degrees C in the pH range of 6.4-6.7 while restricting illumination. Next the specific growth rate, mu, in the batch culture and the fixed dilution rate, D, in the continuous culture were plotted against E(x). The results showed that the relation between D and E(x) can be expressed in a Michaelis-Menten equation, where the maximal specific growth rate is 0.24 h (-1) and the saturation constant is 6.58 kcal/g . h.Cell concentration calculated by substituting the apparent concentration, X(e), of incubated cells and the apparent maintenance constant, M(e), for this equation agreed with that observed in almost all growth phases. Furthermore, from the change of chlorophyll productivity and the relationship between D and E(x) expressed in this equation, it is assumed that E(x) involves the light energy directly utilized in photosynthesis in the cells and that which is converted into, e.g., heat. This equation also indicated that a maximum in the growth yield existed. Then the growth yield of 0.029 g/kcal obtained at the incident light of 1.46 or 2.63 cal/cm(2) . h was maximum (maximal conversion efficiency of light energy, 15.6%).These results indicate that this method of deriving the equation for the growth rate from this study is a useful procedure for obtaining bioengineering findings.