Microbial Oil Production from Alkali Pre-Treated Giant Reed (Arundo donax L.) by Selected Fungi

Abstract

This study aimed to evaluate the microbial oil production by three selected strains, Mortierella isabellina, Cunninghamella echinulata, and Thamnidium elegans, after fermentation of an enzymatic hydrolysate from alkali pre-treated giant reed biomass, in comparison to a semi-synthetic medium, at three increasing nitrogen supplementation levels (0.14, 0.25, and 0.47 g/L). M. isabellina showed the fastest sugar consumption, the highest final cell and oil concentrations (10.9 and 5.6 g/L, respectively), as well as the highest cellular oil content, oil yield/g sugar consumed, and oil productivity (63.4%, 0.19 g/g, and 1 g/L/day, respectively) in the giant reed hydrolysate. The oil yield tended to decrease with an increasing nitrogen content in the cultures. Oleic acid was the most copious fatty acid in the oil for all the fungi. On the contrary, T. elegans exhibited the poorest performances. In particular, M. isabellina showed, respectively, the highest and lowest values of oleic and γ-linolenic acid (52.2 and 3.1%, on average). In comparison, C. echinulata and T. elegans showed much higher γ-linolenic acid content (15.3 and 21.6%, on average). Notably, the C. echinulata cultures showed by far the highest γ-linolenic acid concentration in both substrates (345 and 595 g/L in the giant reed hydrolysate and in the synthetic medium, respectively). Finally, the estimated biodiesel properties of all the oils fell within the limits of the U.S. standards, while the oil of M. isabellina only respected the tighter limits fixed by the E.U. regulations.