Photoperiod-dependent protein and lipid biosynthesis in Auxenochlorella pyrenoidosa cultivated using food waste...

The valorization of food waste hydrolysate (FWH) for microalgal cultivation presents a promising approach to a circular economy. However, the directed regulation of microalgae-based metabolites synthesized using FWH remains a challenge. To address this issue, this study investigated the influence of photoperiods on the regulation of protein and lipid biosynthesis in Auxenochlorella pyrenoidosa with FWH. As expected, it was found that photoperiod significantly redirected carbon and nitrogen flux, thereby selectively enhancing the accumulation of target metabolites. Specifically, a 16:8 h (light/dark) cycle optimized protein biosynthesis and quality, achieving the high essential amino acid ratio and the amino acid score. Conversely, extended dark periods biased metabolism towards lipids, with an 8:16 h (light/dark) cycle yielding the highest lipid productivity of 157.54 mg/L/d. This regime also significantly improved biodiesel properties, including a cetane number of 51.86 and an oxidation stability of 7.54. Physiological and molecular analyses revealed that dark-induced activation of the antioxidant system, along with the concomitant upregulation of key genes involved in hexose transport, NADPH supply, and TAG assembly, underpinned efficient lipid biosynthesis. Overall, the findings demonstrate that photoperiod control is an effective strategy for orchestrating the production of high-quality proteins or lipids from A. pyrenoidosa in FWH, advancing the development of sustainable microalgae-based biorefineries.