Food waste upcycling via microalgal adaptive evolution for lipids and fatty acids enhancement towards circular bioeconomy

Disposal of food waste (FW) has become a significant problem that exacerbates the economy, environment and climate due to its rich nutrient content, thereby implying the necessity to upcycle FW by biotechnology means in a sustainable manner. Employing photosynthetic microalgae to FW upcycling hold great potential to simultaneously remediate the FW and to biosynthesize novel commodity metabolites. However, effective nutrient utilization of FW and metabolite overproduction by native algae is inadequate, and thus further development of strain and strategy is warranted to achieve a circular bioeconomy. Here, the marine Nannochloropsis oceanica was improved by adaptive laboratory evolution (ALE) under low salt conditions for enhanced lipid and uncompromised growth features. Then, FW hydrolysate (FWH) was used as the carbon source to facilitate the mixotrophic cultivation of N. oceanica. Results showed that the biomass of scrutinized evolved cells (ALE70) resulted in enhanced biomass production of 830 mg/l using FWH. Interestingly, ALE70 strains accumulate lipids up to 49 % of total cell dry weight, which was 1.5-fold higher than the WT cells cultivated in FWH. Importantly, FAME analysis by GC–MS showed that FWH provision to the ALE70 strains resulted in notable fatty acid alteration, enriched explicitly with unsaturated fatty acid and EPA content was hiked by 32 % of FAME. Altogether, these findings demonstrated a potential duplex strategy by employing the evolved strains to upcycle the food waste for valuable metabolite biosynthesis effectively and also offer promising insights into algal-associated food waste valorization towards circular bioeconomy.