Physiological studies on microalgal culture additives to optimize growth rate and oil content

Insulin, in nature, has a stimulatory effect on microorganisms. These effects include the acceleration of sugar metabolism, triacylglycerol anabolism, growth rate, and formation of oils. We also observed that insulin may cause indirect activation of triacylglycerol lipase by forcing the cell to permanently require an energy source. Thus, cells can consume all of their accumulated internal fuel sources such as lipids, proteins, and carbohydrates. After studying the effects of using two types of insulin (Humulin 70/30, and human insulin expressed in yeast) at different concentrations on microalgae (Chlorella sp.), we found that with certain concentrations of insulin (1:3.3 ml unit Humulin 70/30 per ml; 1:2.6 ml unit yeast insulin per ml), there was an increase in algal growth rate and decrease in cell size. We therefore studied the effect of insulin under conditions of lipase inhibition by Triton WR 1339 (Tyloxapol), which was used at different concentrations with and without insulin. We found strong regression in the growth rate with increasing Triton concentrations. However, we also observed that the cell size under the effect of Triton and Triton-insulin was larger than the cell size under the effect of insulin alone, and also larger than for control cells. Also, the oil content of the Triton-insulin cells was higher than those of the control cells or the cells under the effect of insulin alone.