Transcriptomic and metabolomic analyses revealed regulation mechanism of mixotrophic Cylindrotheca sp. glycerol utilization and biomass promotion

Abstract

Background Diatoms have been viewed as ideal cell factories for production of some high-value bioactive metabolites, such as fucoxanthin, but their applications are restrained by limited biomass yield. Mixotrophy, by using both CO2 and organic carbon source, is believed effective to crack the bottleneck of biomass accumulation and achieve a sustainable bioproduct supply. Results Glycerol, among tested carbon sources, was proved as the sole that could significantly promote growth of Cylindrotheca sp. with illumination, a so-called growth pattern, mixotrophy. Biomass and fucoxanthin yields of Cylindrotheca sp., grown in medium with glycerol (2 g L−1), was increased by 52% and 29%, respectively, as compared to the autotrophic culture (control) without compromise in photosynthetic performance. As Cylindrotheca sp. was unable to use glycerol without light, a time-series transcriptomic analysis was carried out to elucidate the light regulation on glycerol utilization. Among the genes participating in glycerol utilization, GPDH1, TIM1 and GAPDH1, showed the highest dependence on light. Their expressions decreased dramatically when the alga was transferred from light into darkness. Despite the reduced glycerol uptake in the dark, expressions of genes associating with pyrimidine metabolism and DNA replication were upregulated when Cylindrotheca sp. was cultured mixotrophically. Comparative transcriptomic and metabolomic analyses revealed amino acids and aminoacyl-tRNA metabolisms were enhanced at different timepoints of diurnal cycles in mixotrophic Cylindrotheca sp., as compared to the control. Conclusions Conclusively, this study not only provides an alternative for large-scale cultivation of Cylindrotheca, but also pinpoints the limiting enzymes subject to further metabolic manipulation. Most importantly, the novel insights in this study should aid to understand the mechanism of biomass promotion in mixotrophic Cylindrotheca sp.

Mixotrophic culture enhances fucoxanthin production in the haptophyte Pavlova gyrans

“…The result indicating that mixotrophic media had only a slight effect on photosynthesis is consistent with previous results obtained for the diatoms Phaeodactylum tricornutum and Cylindrotheca sp. (Villanova et al 2017 ; Wang et al 2023 ). Thus, the metabolite levels observed in the CBB cycle of the mixotrophic OPMS 30543X group may have been higher than those in the autotrophic group because of the added glycerol effect.…”

“…Previous studies on P. lutheri have shown that more biomass is produced by mixotrophs than by autotrophs when cultured at appropriate light intensities (Bashir et al 2019 ). Moreover, in fucoxanthin-producing microalgae, HL intensity increases biomass production under autotrophic conditions while reducing fucoxanthin content (Wang et al 2023 ). To achieve maximum biomass and fucoxanthin production under mixed nutrition conditions, we determined the appropriate light intensity for OPMS 30543X.…”