Light intensity and spectral quality modulation for improved growth kinetics and biochemical composition of Chlamydomonas reinhardtii.

Effective strategies to optimize algal growth and lipid productivity are critical for the sustainable production of biomass for various applications. Light management has emerged as a promising approach, but the intricate relationship between light intensity, spectral quality, and algal responses remains poorly understood. This study investigated the effects of different light qualities (blue, red-orange, and white-yellow) and intensities (45-305 µmol/m2·s) on Chlamydomonas reinhardtii. Red-orange light exhibited the highest promotion of biomass growth and lipid productivity, with specific growth rates of 1.968 (d-1) and biomass productivity of 0.284 (g/L/d) at 155 µmol/m2·s and 205 µmol/m2·s, respectively. Within the intensity range of 205 µmol/m2·s to 305 µmol/m2·s, lipid mass fractions ranged from 10.5% w/w to 11.0% w/w, accompanied by lipid concentrations ranging from 68.6 mg/L to 74.9 mg/L. Red-orange light positively influenced carbohydrate accumulation, while blue light promoted protein synthesis. These findings highlight the importance of optimizing light quality and intensity to enhance algal biomass productivity and manipulate biochemical composition. Understanding the complex relationship between light parameters and algal physiology will contribute to sustainable algal cultivation practices and the use of microalgae as a valuable bioresource.

LED alternating between blue and red-orange light improved the biomass and lipid productivity of Chlamydomonas reinhardtii.

Light management is important for improving algae cultivation, specifically by enhancing the productivity of biomass and valued bioproducts. In this study, we present evidence that alternating blue and red-orange light can improve the algal growth kinetics and lipid production in a photobioreactor. Blue (430-445, 460-470 nm) and red-orange light (580-660 nm) from a LED were set at the light saturation point (B: 65 µmol/m2s; RO: 155 µmol/m2s) and alternated for the cultivation of the green alga Chlamydomonas reinhardtii. Growth kinetics, lipid, carbohydrate, and protein content were measured as a function of alternating illumination time. Results reveal that the first illumination light and illumination time had a significant impact on the growth kinetics and nutrient composition. When the red-orange light illumination was used at the beginning of cultivation (RO/B alternation), the biomass concentration and productivity increased 8% and 18% on average, respectively; lipid mass fraction and concentration increased 21-27% and 24-26% when 0.25-0.50 h per day of blue light illumination was used; no significant change of carbohydrate and protein content were observed. Relative to blue light alone, the improvement of growth kinetics, lipid mass fraction and concentration, and the carbohydrate concentration was significant. Under B/RO alternation (when the blue light was used first), on average, the protein content was significantly higher than RO/B alternation.

Interactive effects of light quality and culturing temperature on algal cell size, biomass doubling time, protein content, and carbohydrate content.

Light management strategy can be used to improve algal biomass and nutrient production. However, the response of algal metabolism to different light qualities, especially their interaction with other environmental factors, is not well understood. This study focuses on the interactive effects of light quality and culturing temperature on algal protein content and carbohydrate content of C. reinhardtii. Three LED light sources (blue light, red-orange light, and white-yellow light) were applied to grow algae in batch cultures with a light intensity of 105 µmol/m2s under the temperatures of 24 °C to 32 °C. The protein and carbohydrate content were measured in both the late exponential growth phase and the late stationary growth phase. The results revealed that there was an interactive effect of light quality and culturing temperature on the protein and carbohydrate content. The combined conditions of blue light and a temperature of 24 °C or 28 °C, which induced a larger algal cell size with a prolonged cell cycle and a low division rate, resulted in the highest protein content; the protein mass fraction and concentration were 32% and 52% higher than that under white-yellow light at 32 °C. The combined conditions of red-orange light and a temperature of 24 °C, which promoted both the cell division and size growth, enhanced the carbohydrate content; the carbohydrate mass fraction and concentration were 161% and 155% higher than that under white-yellow light at 24 °C. When there was temperature stress (32 °C) or nutrient stress, the effect of light quality reduced, and the difference of protein and carbohydrate content among the three light qualities decreased. KEY POINTS: • Studied light quality-temperature interactive effect on protein, carbohydrate synthesis. • Protein content was high under low cell division rate. • Carbohydrate content was high under high cell division and cell size growth rate.

Production and characterization of algae extract from Chlamydomonas reinhardtii

Background: Algae offer many advantages as biofuel sources including: high growth rates, high lipid content, the ability to grow on non-agricultural land, and the genetic versatility to improve strains rapidly and produce co-products. Research is ongoing to make algae biofuels a more financially attractive energy option; however, it is becoming evident that the economic viability of algae-based fuels may hinge upon high-value co-products. This work evaluated the feasibility of using a co-product, algae extract, as a nutrient source in cell culture media. Results: Algae extract prepared from autolysed Chlamydomonas reinhardtii was found to contain 3.0% protein, 9.2% total carbohydrate, and 3.9% free α-amino acid which is similar to the nutrient content of commercially available yeast extract. The effects of algae extract on the growth and metabolism of laboratory strains of Escherichia coli and Saccharomyces cerevisiae were tested by substituting algae extract for yeast extract in LB and YPAD growth media recipes. Complex laboratory media supplemented with algae extract instead of yeast extract showed markedly improved effects on the growth and metabolism of common laboratory microorganisms in all cases except ethanol production rates in yeast. Conclusions: This study showed that algae extract derived from C. reinhardtii is similar, if not superior, to commercially available yeast extract in nutrient content and effects on the growth and metabolism of E. coli and S. cerevisiae. Bacto™ yeast extract is valued at USD $0.15-0.35 per gram, if algae extract was sold at similar prices, it would serve as a high-value co-product in algae-based fuel processes.