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Valorizing Red Seaweed Spent Biomass into Reducing Sugars for β-Carotene Production by Rhodotorula paludigena
(2026-05-01)
Kongsinkaew, Chatchol
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Tangsattayatithan, Chutipol
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Chittapun, Supenya
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Phiphatbunyabhorn, Parivat
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Laemthong, Tunyaboon
Seaweed bioactive extraction generates de-extracted residual solids that remain carbohydrate-rich but are often underutilized. This study developed an integrated valorization route for Gracilaria fisheri spent biomass to produce fermentable sugars for β-carotene production by Rhodotorula paludigena CM33. Reducing sugar production was optimized using response surface methodology (Box–Behnken design) by varying reaction time, sulfuric acid concentration, and biomass loading at 90 °C. The predicted optimum (47.39 min, 2.50% (w/v) H<inf>2</inf>SO<inf>4</inf>, and 7.13% (w/v) biomass) yielded 22.41 g/L reducing sugars and was validated experimentally at 22.22 ± 0.19 g/L, indicating that the model reliably predicted reducing sugar production. The optimized condition was scaled up in a 22 L bioreactor with sequential acid hydrolysis followed by enzyme-assisted hydrolysis, increasing reducing sugars from ~30 to ~40 g/L. FTIR and SEM analyses indicated progressive modification of the carbohydrate matrix across processing stages. Batch cultivation of R. paludigena on the hydrolysate showed that ammonium sulfate supplementation significantly increased biomass, whereas β-carotene titers were not significantly different. Repeated-batch operation on non-supplemented hydrolysate sustained production over four cycles with β-carotene titers of 13.75–17.27 mg/L, demonstrating the operational feasibility of the hydrolysate-based system. Overall, this work demonstrates a practical seaweed biorefinery approach to upgrade G. fisheri spent biomass into sugars and carotenoid-rich yeast biomass.
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Characterization of red pigmented yeasts and genes associated with astaxanthin synthesis in Rhodotorula mucilaginosa HL26-1 and Rhodotorula paludigena LL69-1
(2026-01-01)
Hoondee, Patcharaporn
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Tedsree, Nisachon
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Phuengjayaem, Sukanya
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Kingkaew, Engkarat
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Sritularak, Boonchoo
Background: Astaxanthin, a red xanthophyll carotenoid, is a powerful antioxidant, anticancer, and glucose and lipid homeostasis regulator. Some pigmented yeasts belonging to the genus Rhodotorula, the well-known yeast for beta-carotene production, have been reported as natural astaxanthin producers. However, the lack of genomic data on astaxanthin-producing strains within these species hinders the identification of biosynthetic routes, molecular characterization of these pathways, and gene editing applications. Methods: This study explored the diversity and astaxanthin production capability of cultivable pigmented yeast in flower samples. The astaxanthin production ability was inspected by three consecutive methods, including thin-layer chromatography (TLC) for the preliminary step, followed by quantitative spectrophotometry and high-performance liquid chromatography (HPLC) for qualitative validation. The draft genome sequence and astaxanthin-producing genes of astaxanthin-producing yeasts were examined. Results: Twelve of 23 yeasts from floral samples exhibited natural pigmentation, with colors ranging from pinkish-orange to red, and exhibited the potential for astaxanthin synthesis. These yeasts were Rhodotorula paludigena (three strains) and Rhodotorula mucilaginosa (nine strains). Among R. mucilaginosa strains, HL26-1 had the greatest astaxanthin content (104.98 ± 0.13 μg/g DCW) and yield (0.9280 ± 0.0012 mg/L). Strain LL69-1 has the greatest astaxanthin content (251.78 ± 0.27 μg/g DCW) and yield (1.8632 ± 0.0023 mg/L) among R. paludigena strains. The 18.78 Mbp R. mucilaginosa HL26-1 genome includes 5,711 protein-coding genes. Conversely, the R. paludigena LL69-1 genome was 20.99 Mbp, encompassing 6,782 predicted genes. A comprehensive investigation of draft genome sequences of these two strains identified CrtE, CrtYB, CrtI, CrtS, and CrtR as potential astaxanthin transcription genes. Conclusion: Here, our results highlight the outstanding potential of two naturally pigmented yeasts, R. mucilaginosa HL26-1 and R. paludigena LL69-1, for astaxanthin production. Furthermore, our findings provide information on the whole genome and protein-encoded genes associated with astaxanthin production, which serve as valuable biological resources for various biotechnological applications.
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Fed-batch strategies for growing β-carotene enriched yeast Rhodotorula paludigena using untreated molasses
(2025-11-01)
Kongsinkaew, Chatchol
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Chisti, Yusuf
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Ketudat-Cairns, Mariena
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Chittapun, Supenya
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Pornpukdeewattana, Soisuda
The β-carotene-rich yeast Rhodotorula paludigena CM33 was grown in a 22-L bioreactor using sugarcane molasses in combination with several distinct fed-batch strategies: DO (dissolved oxygen)-stat; stepwise feeding; and hybrid feeding (an initial exponential feeding phase followed by a DO-stat operation). The impacts of feeding strategies on biomass production, carotenoid production and nutrient conversion efficiencies were evaluated. The stepwise feeding proved most effective, achieving: a final dry biomass concentration of 73.1 ± 2.7 g L−1; a β-carotene titer of 181.9 ± 1.0 mg L−1; a biomass volumetric productivity of 1.33 ± 0.05 g L−1 h−1; and β-carotene productivity of 3.31 ± 0.02 mg L−1 h−1. However, with this feeding strategy the sugar and nitrogen conversion efficiencies were the lowest: the β-carotene yield on total sugar was 0.92 ± 0.00 mg g−1 and its yield on nitrogen was 5.47 ± 0.06 mg g−1. In contrast, the DO-stat operation was the most resource efficient, providing a biomass yield on sugar of 0.47 ± 0.02 g g−1, a biomass yield on nitrogen of 2.64 ± 0.05 g g−1, a β-carotene yield on sugar of 1.08 ± 0.04 mg g−1, and β-carotene yield on nitrogen of 6.08 ± 0.08 mg g−1. The hybrid strategy resulted in intermediate values of the various performance parameters. Raw sugarcane molasses proved to be excellent for high-cell-density culture of R. paludigena. A compromise between productivity and resource use efficiency may be required for commercial production of β-carotene especially if the substrate is expensive compared to the product.
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Diversity, astaxanthin production, and genomic analysis of Rhodotorula paludigena SP9-15
(2023-07-01)
Phuengjayaem, Sukanya
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Kingkaew, Engkarat
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Hoondee, Patcharaporn
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Rojsitthisak, Pornchai
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Sritularak, Boonchoo
Astaxanthin is a carotenoid known for its powerful antioxidant properties. This study focused on isolating yeast strains capable of producing astaxanthin from flower and fruit samples collected in Thailand. Out of 115 isolates, 11 strains were identified that produced astaxanthin. Molecular identification techniques revealed that these isolates belonged to two species: Rhodotorula paludigena (5 isolates) and Rhodosporidiobolus ruineniae (6 isolates). Whole-genome analysis of one representative strain, R. paludigena SP9-15, identified putative candidate astaxanthin synthesis-associated genes, such as CrtE, CrtYB, CrtI, CrtS, CrtR, CrtW, CrtO, and CrtZ. High-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) confirmed astaxanthin production. Further optimization of astaxanthin production was carried out by investigating the effects of various factors on the growth rate and astaxanthin production. The optimal conditions were 40 g/L glucose as a carbon source, pH 7.5, and cultivation at 25 °C with 200 rpm for 3 days. Under these conditions, R. paludigena SP9-15 synthesized biomass of 11.771 ± 0.003 g/L, resulting in astaxanthin with a content of 0.558 ± 0.018 mg/g DCW (dry cell weight), an astaxanthin yield of 6.565 ± 0.238 mg/L, and astaxanthin productivity of 2.188 ± 0.069 g/L/day. These findings provide insights into astaxanthin production using red yeast strains from Thailand and highlight the potential of R. paludigena SP9-15 for further application.

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