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

Optimizing Phaeodactylum tricornutum cultivation: integrated strategies for enhancing biomass, lipid, and fucoxanthin production

BACKGROUND

Phaeodactylum tricornutum is a versatile marine microalga renowned for its high-value metabolite production, including omega-3 fatty acids and fucoxanthin, with emerging potential for integrated biorefinery approaches that encompass biofuel and bioproduct generation. Therefore, in this study we aimed to optimize the cultivation conditions for boosting biomass, lipid, and fucoxanthin production in P. tricornutum, focusing on the impacts of different nutrient ratios (nitrogen, phosphorus, silicate), glycerol supplementation, and light regimes.

RESULTS

Optimized medium (- 50%N%, + 50% P, Zero-Si, 2 g glycerol) under low-intensity blue light (100 μmol m⁻2 s⁻1) improved biomass to 1.6 g L⁻1, with lipid productivity reaching 539.25 mg g⁻1, while fucoxanthin increased to 20.44 mg g-1. Total saturated fatty acid (ΣSFA) content in the optimized culture increased approximately 2.4-fold compared to the control F/2 medium. This change in fatty acid composition led to improved biodiesel properties, including a higher cetane number (59.18 vs. 56.04) and lower iodine value (53.96 vs 88.99 g I2/100 g oil). The optimized conditions also altered the biodiesel characteristics, such as kinematic viscosity, cloud point, and higher heating value.

CONCLUSION

Our optimization approach reveals the significant potential of P. tricornutum as a versatile microbial platform for biomass, lipid, and fucoxanthin production. The tailored cultivation strategy successfully enhanced biomass and lipid accumulation, with notable improvements in biodiesel properties through strategic nutrient and light regime manipulation. These findings demonstrate the critical role of precise cultivation conditions in optimizing microalgal metabolic performance for biotechnological applications.

Mixotrophic culture enhances fucoxanthin production in the haptophyte Pavlova gyrans

Fucoxanthin is a versatile substance in the food and pharmaceutical industries owing to its excellent antioxidant and anti-obesity properties. Several microalgae, including the haptophyte Pavlova spp., can produce fucoxanthin and are potential industrial fucoxanthin producers, as they lack rigid cell walls, which facilitates fucoxanthin extraction. However, the commercial application of Pavlova spp. is limited owing to insufficient biomass production. In this study, we aimed to develop a mixotrophic cultivation method to increase biomass and fucoxanthin production in Pavlova gyrans OPMS 30543X. The effects of culturing OPMS 30543X with different organic carbon sources, glycerol concentrations, mixed-nutrient conditions, and light intensities on the consumption of organic carbon sources, biomass production, and fucoxanthin accumulation were analyzed. Several organic carbon sources, such as glycerol, glucose, sucrose, and acetate, were examined, revealing that glycerol was well-consumed by the microalgae. Biomass and fucoxanthin production by OPMS 30543X increased in the presence of 10 mM glycerol compared to that observed without glycerol. Metabolomic analysis revealed higher levels of the metabolites related to the glycolytic, Calvin-Benson-Bassham, and tricarboxylic acid cycles under mixotrophic conditions than under autotrophic conditions. Cultures grown under mixotrophic conditions with a light intensity of 100 µmol photons m-2 s-1 produced more fucoxanthin than autotrophic cultures. Notably, the amount of fucoxanthin produced (18.9 mg/L) was the highest reported thus far for Pavlova species. In conclusion, the use of mixotrophic culture is a promising strategy for increasing fucoxanthin production in Pavlova species. KEY POINTS: • Glycerol enhances biomass and fucoxanthin production in Pavlova gyrans • Metabolite levels increase under mixotrophic conditions • Mixotrophic conditions and medium-light intensity are appropriate for P. gyrans.

One-step bioremediation of hypersaline and nutrient-rich food industry process water with a domestic microbial community containing diatom Halamphora coffeaeformis

Proper treatment of hypersaline and nutrient-rich food industry process water (FIPW) is challenging in conventional wastewater plants. Insufficient treatment leads to serious environmental hazards. However, bioremediation of FIPW with an indigenous microbial community can not only recover nutrients but generate biomass of diverse applications. In this study, monoculture of Halamphora coffeaeformis, together with synthetic bacteria isolated from a local wastewater plant, successfully recovered 91% of NH4+-N, 78% of total nitrogen, 95% of total phosphorus as well as 82% of total organic carbon from medium enriched with 10% FIPW. All identified organic acids and amino acids, except oxalic acid, were completely removed after 14 days treatment. A significantly higher biomass concentration (1.74 g L-1) was achieved after 14 days treatment in the medium with 10% FIPW than that in a nutrient-replete lab medium as control. The harvested biomass could be a potential feedstock for high-value biochemicals and fertilizer production, due to fucoxanthin accumulation (3 mg g-1) and a fantastic performance in P assimilation. Metagenomic analysis revealed that bacteria community in the algal system, dominated by Psychrobacter and Halomonas, also contributed to the biomass accumulation and uptake of nutrients. Transcriptomic analysis further disclosed that multiple pathways, involved in translation, folding, sorting and degradation as well as transport and catabolism, were depressed in H. coffeaeformis grown in FIPW-enriched medium, as compared to the control. Collectively, the proposed one-step strategy in this work offers an opportunity to achieve sustainable wastewater management and a way towards circular economy.