Breeding of Chlorella mutants deficient in chlorophyll synthesis and evaluation of its protein yield and quality / 生物工程学报

The aim of this study was to construct Chlorella mutants deficient in chlorophyll synthesis by atmospheric pressure room temperature plasma (ARTP) mutagenesis, and screen novel algal species with very low chlorophyll content which is suitable for protein production by fermentation. Firstly, the lethal rate curve of mixotrophic wild type cells was established by optimizing the mutagenesis treatment time. The mixotrophic cells in early exponential phase were treated by the condition of over 95% lethal rate, and 4 mutants with the visual change of colony color were isolated. Subsequently, the mutants were cultured in shaking flasks heterotrophically for evaluation of their protein production performance. P. ks 4 mutant showed the best performance in Basal medium containing 30 g/L glucose and 5 g/L NaNO3. The protein content and productivity reached 39.25% dry weight and 1.15 g/(L·d), with an amino acid score of 101.34. The chlorophyll a content decreased 98.78%, whereas chlorophyll b was not detected, and 0.62 mg/g of lutein content made the algal biomass appear golden yellow. This work provides a novel germplasm, the mutant P. ks 4 with high yield and high quality, for alternative protein production by microalgal fermentation.

Fatty Acid Biosynthesis from Chlorella in Autotrophic and Mixotrophic Cultivation

Abstract Microalgae are photosynthetic microorganisms whose composition and biomass production can be influenced by manipulating the cultivation conditions employed. However, few studies have evaluated the effects of various cultivation conditions in autotrophic and mixotrophic conditions. The present work aimed to evaluate the effects of cultivation conditions on the cell growth and biosynthesis of fatty acids (FAs) by microalgae of the genus Chlorella in autotrophic and mixotrophic cultivation. Evaluation of the effects of the conditions was performed using an experimental design methodology. The highest values of maximum biomass concentration (Xmax) and maximum biomass productivity (Pmax) were obtained in autotrophic cultures. Palmitic acid was the FA obtained at the highest concentration in both cultivation modes. The concentrations of polyunsaturated FAs (PUFAs) ranged from 12.2 to 41.2% in autotrophic cultures and from 11 to 34.3% in the mixotrophic cultures. The variables photoperiod and sodium bicarbonate concentration showed the greatest influence on the Xmax, Pmax, and PUFA concentration in autotrophic and mixotrophic cultivations, respectively. This study verified that the selection of conditions and mode of cultivation contribute to the production of microalgal biomass and FA biosynthesis.

Controlled introduction of selenium into Chlorella cells.

Selenium (Se) is an important element in the antioxidant system of the human body, and Chlorella, well-known for its therapeutic effects, is the ideal carrier to offer it in the wanted organic form. The kinetics of Se absorption by growing algal cells and its distribution in the cells are studied using radioactive 75Se labelled solutions. There is a rapid Se absorption within the first few minutes at the cell surfaces where it is irreversibly fixed and cannot be absorbed by the human body. In the final state, reached after 24-48 hr, about 40% of the total fixed Se is inside the cells in the wanted organic-bound form.