Microalgae are primary producers with high photosynthetic efficiency and strong environmental adaptability, and their intracellular polysaccharides (IPs) are rich in reactive hydroxyl and carboxyl groups, giving them potential for antioxidant, immunomodulatory and food-additive applications. Desert microalgae are particularly noteworthy: long-term adaptation to drought, high-intensity light and severe diurnal temperature fluctuations has reprogrammed their metabolism, enabling them to produce polysaccharides with structural and functional characteristics distinct from those of freshwater and marine species.
A research team led by Fulong Chen at Shihezi University in Xinjiang, China, recently investigated how exogenous carbon input reshapes sugar metabolism and IP properties in the desert * Chlorella * sp. GTD4C-2. The strain was isolated from the Gurbantunggut Desert. The team cultured the alga at 28 °C and 2,500 lx under a 12 h:12 h light–dark cycle: the control group was grown photoautotrophically in Bold's basal medium, while the treatment groups received 10 g/L sodium acetate or glucose as an exogenous carbon source. The researchers then used gas chromatography–mass spectrometry to analyze targeted sugar metabolites at the logarithmic growth phase, applied orthogonal partial least-squares discriminant analysis to screen for differential metabolites, and extracted IPs with 4% NaOH to determine their monosaccharide composition and in vitro antioxidant activity.
The addition of exogenous carbon significantly altered growth kinetics. Under photoautotrophic conditions, the strain showed pronounced growth delay, whereas the addition of sodium acetate or glucose advanced the onset of the logarithmic growth phase to days 6–8 and increased the exponential-phase growth rates to (5.85 ± 0.19) and (5.70 ± 0.10) mg/(L·d), respectively—approximately 2.8 times the autotrophic rate of (1.50 ± 0.13) mg/(L·d).
Metabolomic analysis identified 11 monosaccharides that accumulated differentially across the three culture conditions, with sucrose and D-galactose showing the most significant changes. KEGG pathway analysis indicated that the differences were mainly enriched in starch and sucrose metabolism, the pentose phosphate pathway (PPP) and galactose metabolism. Trehalose was detected only in the glucose-supplemented cultures, consistent with a trehalose-6-phosphate–hexokinase regulatory circuit activated under high glucose input; meanwhile, galactose accumulation was suppressed in the glucose group.
These metabolic changes were reflected in IP composition. IPs from all culture groups contained glucose, ribose and galactose, but glucose content was lowest in photoautotrophic cells, at (0.213 ± 0.096) mg/g, and significantly higher in the sodium acetate group (0.769 mg/g) and the glucose group (0.607 mg/g).
Antioxidant activity showed the opposite trend. IPs from photoautotrophic cultures achieved a DPPH radical scavenging rate of (85.10 ± 0.09)% and a hydroxyl radical scavenging rate of (31.00 ± 0.89)% at 0.2 mg/mL, outperforming IPs from the exogenous-carbon-supplemented cultures; moreover, scavenging activity increased with polysaccharide concentration in a dose-dependent manner.
"What surprised us was that the fastest-growing culture group did not produce the most antioxidant polysaccharides," said Lu Wang, first author of the study and a master's student at the College of Life Sciences, Shihezi University. "Exogenous carbon reshaped the central carbon flux—particularly the pentose phosphate pathway and galactose metabolism pathway—and this remodeling changed the monosaccharide composition of the polysaccharides. The lower glucose proportion in the photoautotrophic IPs appears to expose more reactive hydroxyl and carboxyl sites, thereby enhancing radical scavenging capacity."
The authors propose a mechanistic chain linking carbon input to function: exogenous carbon drives the redistribution of metabolic fluxes, which in turn alters the monosaccharide composition and glycosidic linkage patterns of IPs, ultimately determining antioxidant capacity. They also speculate that the PPP–NADPH axis may indirectly support glutathione-mediated hydroxyl radical scavenging in photoautotrophic cells, although this possibility requires further verification. Glycosidic bond conformation and sulfation modification were not directly measured in this study, and these remain issues to be addressed in future work.
"Ultimately, we hope to use carbon source strategies—such as limiting the amount of glucose added—to direct desert microalgal polysaccharides toward defined structures and stronger bioactivity," Wang said. "This strain from the Gurbantunggut Desert is a promising resource for functional products such as antioxidant ingredients and nutritional fortifiers."
Microbiology China
10.13344/j.microbiol.china.251339
Physicochemical and polysaccharide properties of desert Chlorella sp. GTD4C-2 upon addition of different exogenous carbon sources under light conditions
20-Oct-2026