Enhancing fucoxanthin production in Phaeodactylum tricornutum by photo-fermentation / 生物工程学报

The aim of this study was to develop a technical system for high-efficient production of fucoxanthin by photo-fermentation of Phaeodactylum tricornutum. In a 5 L photo-fermentation tank, the effects of initial light intensity, nitrogen source and concentration as well as light quality on biomass concentration and fucoxanthin accumulation in P. tricornutum were investigated systematically under mixotrophic condition. The results showed that the biomass concentration, fucoxanthin content and productivity reached the highest level of 3.80 g/L, 13.44 mg/g and 4.70 mg/(L·d) under the optimal conditions of initial light intensity of 100 μmol/(m2·s), 0.02 mol TN/L of tryptone: urea (1:1, N mol/N mol) as mixed nitrogen source, and a mixed red/blue (R: B=6:1) light, 1.41, 1.33 and 2.05-fold higher than that before optimization, respectively. This study developed a key technology for enhancing the production of fucoxanthin by photo-fermentation of P. tricornutum, facilitating the development of marine natural products.

High efficient assimilation of NO₃⁻-N with coproduction of microalgal proteins by Chlorella pyrenoidosa / 生物工程学报

The aim of this study was to establish a novel technology using microalgae for NO₃⁻ removal from high concentration wastewater and conversion to algal proteins. The effects of cultivation modes and illumination modes on the biomass yield, NO₃⁻ assimilation rate and algal protein yield were first investigated in shaking flasks for mixotrophic cultivation of Chlorella pyrenoidosa, and subsequently the scale-up verification in 5-L photo fermenter was successfully conducted. Fed-batch cultivation without medium recycling was the best cultivation mode in shaking flask system, in which the highest biomass yield (35.95 g/L), the average NO₃⁻ assimilation rate (2.06 g/(L·d)) and algal protein content (up to 42.44% of dry weight) were achieved. By using a staged increase of light intensity as illumination modes, the specific growth rate of cells could be significantly promoted to the highest (0.65 d⁻¹). After a 128-hour continuous cultivation in a 5-L photo fermenter, the highest biomass yield and the average NO₃⁻ assimilation rate were reached to 66.22 g/L and 4.38 g/(L·d) respectively, with the highest algal protein content at 47.13% of dry weight. Our study could provide a photo fermentation technology of microalgae for highly efficient treatment of waste industrial nitric acid and/or high concentration nitrate wastewater. This microalgae-based bioconversion process could coproduce protein-rich microalgal biomass, which facilitates the resource utilization of these type wastewater by trash-to-treasure conversion.

Photo-fermentational hydrogen production of Rhodobacter sp. KKU-PS1 isolated from an UASB reactor

Background In this study, the detection of nifH and nifD by a polymerase chain reaction assay was used to screen the potential photosynthetic bacteria capable of producing hydrogen from five different environmental sources. Efficiency of photo-hydrogen production is highly dependent on the culture conditions. Initial pH, temperature and illumination intensity were optimized for maximal hydrogen production using response surface methodology with central composite design. Results Rhodobacter sp. KKU-PS1 (GenBank Accession No. KC478552) was isolated from the methane fermentation broth of an UASB reactor. Malic acid was the favored carbon source while Na-glutamate was the best nitrogen source. The optimum conditions for simultaneously maximizing the cumulative hydrogen production (Hmax) and hydrogen production rate (Rm) from malic acid were an initial of pH 7.0, a temperature of 25.6°C, and an illumination intensity of 2500 lx. Hmax and Rm levels of 1264 ml H2/l and 6.8 ml H2/L-h were obtained, respectively. The optimum initial pH and temperature were further used to optimize the illumination intensity for hydrogen production. An illumination intensity of 7500 lx gave the highest values of Hmax (1339 ml H2/l) and Rm (12.0 ml H2/L-h) with a hydrogen yield and substrate conversion efficiency of 3.88 mol H2/mol malate and 64.7%, respectively. Conclusions KKU-PS1 can produce hydrogen from at least 8 types of organic acids. By optimizing pH and temperature, a maximal hydrogen production by this strain was obtained. Additionally, by optimizing the light intensity, Rm was increased by approximately two fold and the lag phase of hydrogen production was shortened.