Weining Chen’s research while affiliated with Nanyang Technological University and other places

Microalgae used for CO2 biofixation can effectively relieve CO2 emissions and produce high-value biomass to achieve “waste-to-treasure” bioconversion. However, the low CO2 fixation efficiency and the restricted application of biomass are currently bottlenecks, limiting the economic viability of CO2 biofixation by microalgae. To achieve high-efficient CO2 fixation and high-protein biomass production, the oleaginous microalga Coccomyxa subellipsoidea (C. subellipsoidea) was cultivated autotrophically through optimizing inorganic carbon and nitrogen supply. 0.42 g L⁻¹ NaHCO3 supplemented with 2% CO2 as a hybrid carbon source resulted in high biomass concentration (3.89 g L⁻¹) and productivity (318.33) with CO2 fixation rate 544.21 mg L⁻¹ d⁻¹ in shake flasks. Then, used in a 5-L photo-fermenter, the maximal protein content (60.93% DW) in batch 1, and the highest CO2 fixation rate (1043.95 mg L⁻¹ d⁻¹) with protein content (58.48% DW) in batch 2 of repeated fed-batch cultures were achieved under 2.5 g L⁻¹ nitrate. The relative expression of key genes involved in photosynthesis, glycolysis, and protein synthesis showed significant upregulation. This study developed a promising approach for enhancing carbon allocation to protein synthesis in oleaginous microalga, facilitating the bioconversion of the fixed carbon into algal protein instead of oil in green manufacturing.

To achieve ultrahigh-efficient ammonium removal and valuable biomass coproduction, Chlorella-mediated short-time acclimation was implemented in photo-fermentation. The results demonstrated short-time acclimation of mixotrophic Chlorella pyrenoidosa could significantly improve NH4⁺ removal and biomass production in shake flasks. After acclimation through two batch cultures in 5-L photo-fermenter, the maximum NH4⁺ removal rate (1,400 mg L⁻¹ d⁻¹) were achieved under high NH4⁺ level (4,750 mg L⁻¹) in batch 3. In 50-L photo-fermenter, through one batch acclimated culture, the maximum NH4⁺ removal rate (2,212 mg L⁻¹ d⁻¹) and biomass concentration (58.4 g L⁻¹) were achieved in batch 2, with the highest productivities of protein (5.56 g L⁻¹ d⁻¹) and total lipids (5.66 g L⁻¹ d⁻¹). The hypothetical pathway of nutrients assimilation in mixotrophic cells as cell factory was proposed with detailed discussion. This study provided a novel strategy for high-ammonium wastewater treatment without dilution, facilitating the algae-based “waste-to-treasure” bioconversion process for green manufacturing.

Microbial biomass which mostly generated from the microbial processes of bacteria, yeasts, and microalgae is an important resource. Recent concerns in microbial biomass production field, especially microbial lipid production for biofuel, have been focused towards the mixed culture of microalgae and yeast. To more comprehensive understanding of the mixed culture for microbial biomass, mono Chlorella pyrenoidosa, mono Yarrowia lipolytica and the mixed culture were investigated in the present work. Results showed that the mixed culture achieved significantly faster cell propagation of microalga and yeast, smaller individual cell size of yeast and higher relative chlorophyll content of microalga. The mixed culture facilitated the assimilation of carbon and nitrogen and drove the carbon flow to carbohydrate. Besides higher lipid yield (0.77 g/L), higher yields of carbohydrates (1.82 g/L), protein (1.99 g/L) and heating value (114.64 kJ/L) indicated the microbial biomass harvested from the mixed culture have more potential utilization in renewable energy, feedstuff, and chemical industry.

Microbial biomass which mostly generated from the microbial processes of bacteria, yeasts, and microalgae is an important resource. Recent concerns in microbial biomass production field, especially microbial lipid production for biofuel, have been focused towards the mixed culture of microalgae and yeast. To more comprehensive understanding of the mixed culture for microbial biomass, mono Chlorella pyrenoidosa, mono Yarrowia lipolytica and the mixed culture were investigated in the present work. Results showed that the mixed culture achieved significantly faster cell propagation of microalga and yeast, smaller individual cell size of yeast and higher relative chlorophyll content of microalga. The mixed culture facilitated the assimilation of carbon and nitrogen and drove the carbon flow to carbohydrate. Besides higher lipid yield (0.77 g/L), higher yields of carbohydrates (1.82 g/L), protein (1.99 g/L) and heating value (114.64 kJ/L) indicated the microbial biomass harvested from the mixed culture have more potential utilization in renewable energy, feedstuff, and chemical industry.

To determine the feasibility of microalgae-yeast mixed culture using the liquid digestate of dairy wastewater (LDDW) for biofuels and single cell protein (SCP) production, the cell growth, nutrient removal and outputs evaluation of the mono and mixed culture of Chlorella vulgaris and Yarrowia lipolytica in LDDW were investigated by adding glycerol as carbon source. The results showed that the mixed culture could enhance the biological utilization efficiency of nitrogen and phosphorus, and obtain higher yield of biomass (1.62 g/L), lipid (0.31 g/L), protein (0.51 g/L), and higher heating value (34.06 KJ/L). Compared with the mono culture of C. vulgaris, a decline of the transcription level in nitrate reductase and glutamine synthetase II genes in C. vulgaris was observed in the mixed culture when ammonia was sufficient. The results suggest the possibility of using the mixed culture for the efficient treatment of LDDW and resources recycling.