Direct Production of Biodiesel from the Fungus M. circinelloides; Opportunity to Enhance Yield with Genetic Engineering

Researchers in Spain have demonstrated the direct transformation of biomass consisting of the fungus M. circinelloides into biodiesel compliant with ASTM D6751 and EN14213 and 14214 standards. A paper on their work was published online 2 April in the ACS journal Energy & Fuels.

Oils from oleaginous microorganisms, such as yeasts, fungi, bacteria, and microalgae, are under investigation as alternatives to plant—and especially food crop—oils as feedstocks for renewable fuels and chemicals. Algae are especially of interest because of their ability to capture CO₂ in lipids, but cost-effective, large scale production is still problematic, note Vicente et al. in their paper. Furthermore, not all oleaginous microorganisms have ideal lipid profiles for biodiesel production.

On the other hand, lipid profiles could be modified by genetic engineering in some oleaginous microorganisms, such as the fungus Mucor circinelloides, which has powerful genetic tools. We show here that the biomass from submerged cultures of the oleaginous fungus M. circinelloides can be used to produce biodiesel by acid-catalyzed direct transformation, without previous extraction of the lipids. Direct transformation, which should mean a cost savings for biodiesel production, increased lipid extraction and demonstrated that structural lipids, in addition to energy storage lipids, can be transformed into FAMEs.

—Vicente et al.

The team grew M. circinelloides (strain MU241) in a liquid medium containing glucose as a carbon source (20 g/L). Under experimental conditions, the fungus grew very quickly because it consumed all of the available glucose and stopped growing in the first 48 hours after inoculation. After 96 h, they obtained 4.17 ± 0.25 g/L fungal biomass with a total lipid
content of 22.9 ± 0.9% dry mass.

The saponifiable lipids (those that can be transformed into FAMEs)
and free fatty acids (including energy storage and structural
lipids) were 98.0 ± 1.3% of the total lipids extracted from the biomass.

Because of the high concentration of free fatty acids (3.6 ± 0.6%) in M