A waste upcycling loop: Two-factor adaptive evolution of microalgae to increase polyunsaturated fatty acid production using food waste

The stagnant supply of wild stocks of deep-sea fish and the potential bioaccumulation of toxic pollutants have promoted the research on more sustainable alternatives for the production of valuable polyunsaturated fatty acids (PUFAs) for human supplements. The diatom Phaeodactylum tricornutum has emerged as a promising alternative to oils from deep-sea fish for PUFA production. However, the level of PUFA production by native microalgal strains is not high enough for commercial applications. Improved phenotypes of native microalgal species are urgently required to fulfil commercial demands and achieve economic and environmental sustainability. In this study, we subjected wild-type P. tricornutum to a two-factor adaptive evolution process to successfully generate an evolved strain, ALE-Pt1, with enhanced biomass and PUFA production capabilities under high-glucose conditions. We used food waste hydrolysate as a primary negligible-value carbon source and a substitute for purified glucose for ALE-Pt1 cultivation under mixotrophic conditions, to improve biomass yield and PUFA production. The semi-continuous fermentation of ALE-Pt1 using food waste resulted in the production of 7.8 g of biomass and 0.87 g of eicosapentaenoic acid from a 2.8-L culture volume in a 2-L bioreactor. This microalgae-based food waste upcycling loop, combined with an adaptive evolution process, is a promising PUFA production strategy. Our results provide novel insights into PUFA production via sustainable microalgal-based waste valorisation.