A novel investigation of the growth and lipid production of the extremophile microalga Coccomyxa melkonianii SCCA 048 under the effect of different cultivation conditions: Experiments and modeling

In the present study, the effect of nitrogen manipulation on the growth of the extremophile microalgal strain Coccomyxa melkonianii SCCA 048 was investigated for the first time to study its ability to produce marketable products, such as lipids. To identify the best strategies for cultivating this alga in large scale systems, the nitrate- and pH-dependent growth kinetics and the corresponding kinetic parameters were first evaluated in a multiwell screening. Subsequently, the effects of initial nitrogen concentration on the growth rate, nitrate uptake, as well as the synthesis of lipids and their corresponding quality, were investigated in batch photobioreactors. The experimental results were then successfully interpreted by a simple, albeit novel and exhaustive, mathematical model which takes into account the effects of light intensity, nitrate concentration and pH on the growth and lipid synthesis of this strain. By assessing the pH-dependent kinetics, it was confirmed that Coccomyxa melkonianii is extremophile as far as pH conditions are concerned. Moreover, the obtained growth rates and lipid productivities were high enough to permit sustainable cultivation at large scale. In particular, a quite interesting lipid content (about 40 %wt) was achieved under nitrogen starvation conditions. The fatty acids obtained by transesterification of the extracted lipids might be potentially exploited in different industrial sectors. In addition, the proposed model represents a first step towards the development of a useful tool for the optimization and the design of raceway-type bioreactor where Coccomyxa melkonianii would be cultivated.