Synthesis of single cell oil via de novo and ex novo from Aspergillus Niger mya 135 under submerged fermentation: impact of microparticles

Abstract

Fungal biofactories are well established in industries. Thus, the synthesis of single cell oil from organic wastes constitutes an attractive topic for research toward a biorefinery concept within the demanded circular economy. As an example, microbial lipids are interesting for biodiesel production due to the independence from seasonal and climatic changes, the fast production rate, the minimal labor requirements, and the easy scale-up for industrial processing. Oleaginous microorganisms are capable of produce oil via de novo and ex novo pathways using hydrophilic and hydrophobic substrates, respectively. In addition, productivities of filamentous fungi in submerged fermentation are often associated with specific morphological forms. Thus, in order to control fungal morphology several strategies have been reported. One of these allows the control of growth physically by blocking the aggregation of filamentous microorganisms using microparticles such as talc, aluminium oxide, titanium silicom oxide, and forsterite. In the present work, the native Aspergillus niger ATCC MYA 135 was used to explore its potential to accumulate lipids in the presence of waste cooking oil or waste glycerol as feedstocks. Shake flask fermentation were conducted with or without supplementation of talc. Firstly, biomass samples withdrawn at periodic intervals were stained using Sudan Black and observed at 100X magnification under a light microscope. Interestingly, we found that microparticles performance depended on the organic waste utilized. Adding talc to culture medium not only favored the single cell oil synthesis under ex novo culture condition but also changed the fungal morphology radically. Microparticles modified both size and shape of mycelial objects. On the contrary, the presence of talc decreased the microbial oil accumulation in culture medium formulated with waste glycerol. In relation to the macroscopic fungal morphology, under de novo culture condition, microparticles did not significantly alter the mycelial shape observing hairy and irregular structures sometimes growing out of their centers. Secondly, microbial oils obtained from biomass developed from both feedstocks were extracted using the Folch method. It was found that A. niger MYA was able to accumulate more than 25 % (w/w) of lipids per dry weight. Finally, lipids extracted from biomass grown in culture medium formulated with either hydrophilic or hydrophobic substrate were separated by thin layer chromatography observing the spot corresponding to triacylglycerol. In summary, these findings highlighted that microparticles could impact not only on fungal morphology but also on metabolite production. In addition, our results also showed that medium composition always has to be taken into account when evaluating the impact of microparticles on processes involving filamentous fungi.