Medium acidification and redox imbalance drive triacylglycerol hyperaccumulation in Chlorella sorokiniana.

Authors

Seungwoo Shin, Bae Young Choi, Jaehyun Song, Sujeong Je, Yoomi Roh, Eunbi Kim, Takashi Yamano, Yonghua Li-Beisson, Donghwan Shim, Yasuyo Yamaoka

Published in

Bioresource technology. Pages 136249. Nov 14, 2026. Epub Nov 14, 2026.

Abstract

Carbon and nitrogen availability regulate microalgal lipid production, but conventional induction by nutrient starvation restricts growth. We investigated the physiological and metabolic basis of triacylglycerol (TAG) hyperaccumulation in Chlorella sorokiniana UTEX 2714 under glucose- and ammonium-containing conditions without nitrogen starvation, while ammonium uptake was maintained during early cultivation. TAG accumulation in glucose- and ammonium-containing Tris-glucose-phosphate medium (TGP NH₄⁺) increased 62.8-fold relative to that in glucose- and nitrate-containing medium (TGP NO₃^-) and reached levels comparable to or exceeding those under nitrogen starvation. TAG accumulation was accompanied by gradual medium acidification to approximately pH 3. Preventing acidification strongly suppressed TAG accumulation, whereas initial adjustment to low pH induced only limited TAG accumulation, identifying gradual acidification as a key process parameter rather than low pH alone as a sufficient trigger. We assembled its genome to enable mechanistic analysis. Genome-guided transcriptomic analysis revealed remodeling of carbon and lipid metabolism, including upregulation of fatty acid and TAG biosynthesis genes, together with an increased fraction of reduced nicotinamide adenine dinucleotide phosphate (NADPH) in the total NADP(H) pool and reduced starch accumulation. TGP NH₄⁺ cultivation also caused progressive cell death from 36 to 48 h, whereas inhibition of photosynthetic electron transport or dark incubation improved cell recovery, implicating light-dependent oxidative stress in cytotoxicity. TAG hyperaccumulation was reproduced in 3-L bioreactor cultures. Together, these results establish a physiological basis linking gradual medium acidification, metabolic reprogramming, and redox imbalance to TAG hyperaccumulation under nutrient-replete conditions, providing a basis for optimizing lipid production without nutrient starvation.

PMID:
43034000
Bibliographic data and abstract were imported from PubMed on 15 Nov 2026.

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