Improving light and CO2 availability to enhance the growth rate of the diatom, Chaetoceros muelleri

Mapping the field of microalgae CO2 sequestration: a bibliometric analysis

Microalgae CO₂ sequestration has gained considerable attention in the last three decades as a promising technology to slow global warming caused by CO₂ emissions. To provide a comprehensive and objective analysis of the research status, hot spots, and frontiers of CO₂ fixation by microalgae, a bibliometric approach was recently chosen for review. In this study, 1561 articles (1991-2022) from the Web of Science (WOS) on microalgae CO₂ sequestration were screened. A knowledge map of the domain was presented using VOSviewer and CiteSpace. It visually demonstrates the most productive journals (Bioresource Technology), countries (China and USA), funding sources, and top contributors (Cheng J, Chang JS, and their team) in the field of CO₂ sequestration by microalgae. The analysis also revealed that research hotspots changed over time and that recent research has focused heavily on improving carbon sequestration efficiency. Finally, commercialization of carbon fixation by microalgae is a key hurdle, and supports from other disciplines could improve carbon sequestration efficiency.

Light induces peridinin and docosahexaenoic acid accumulation in the dinoflagellate Durusdinium glynnii

Peridinin is a light-harvesting carotenoid present in phototrophic dinoflagellates and has great potential for new drug applications and cosmetics development. Herein, the effects of irradiance mediated by light-emitting diodes on growth performance, carotenoid and fatty acid profiles, and antioxidant activity of the endosymbiotic dinoflagellate Durusdinium glynnii were investigated. The results demonstrate that D. glynnii is particularly well adapted to low-light conditions; however, it can be high-light-tolerant. In contrast to other light-harvesting carotenoids, the peridinin accumulation in D. glynnii occurred during high-light exposure. The peridinin to chlorophyll-a ratio varied as a function of irradiance, while the peridinin to total carotenoids ratio remained stable. Under optimal irradiance for growth, there was a peak in docosahexaenoic acid (DHA) bioaccumulation. This study contributes to the understanding of the photoprotective role of peridinin in endosymbiont dinoflagellates and highlights the antioxidant activity of peridinin-rich extracts. KEY POINTS: • Peridinin has a protective role against chlorophyll photo-oxidation • High light conditions induce cellular peridinin accumulation • D. glynnii accumulates high amounts of DHA under optimal light supply.

Investigating the impact of light quality on macromolecular composition of Chaetoceros muelleri

Diatoms (Bacillariophyceae) are important to primary productivity of aquatic ecosystems. This algal group is also a valuable source of high value compounds that are utilised as aquaculture feed. The productivity of diatoms is strongly driven by light and CO2 availability, and macro- and micronutrient concentrations. The light dependency of biomass productivity and metabolite composition is well researched in diatoms, but information on the impact of light quality, particularly the productivity return on energy invested when using different monochromatic light sources, remains scarce. In this work, the productivity return on energy invested of improving growth rate, photosynthetic activity, and metabolite productivity of the diatom Chaetoceros muelleri under defined wavelengths (blue, red, and green) as well as while light is analysed. By adjusting the different light qualities to equal photosynthetically utilisable radiation, it was found that the growth rate and photosynthetic oxygen evolution was unchanged under white, blue, and green light, but it was lower under red light. Blue light improved the productivity return on energy invested for biomass, total protein, total lipid, total carbohydrate, and in fatty acids production, which would suggest that blue light should be used for aquaculture feed production.

Cultivation of Microalgae in Unsterile Malting Effluent for Biomass Production and Lipid Productivity Improvement

Microalgae have the potential to grow in nutrient-rich environments and have the ability to accumulate nutrients from wastewater. The nutrients in malting wastewater are ideal for microalgae cultivation. However, there is limited published work on the growth characteristics of freshwater microalgae grown in malting effluent. This study examined the potential of diluted malting effluent for the growth of freshwater green algae Chlorella sp. and Chlamydomonas sp. isolated from northern Ontario and subsequent biomass and lipid production. Under the 18:6 h light/dark cultivation cycle, the highest cell number counted (540 × 104 cell·mL−1 on day 20) and total chlorophyll content were found in 50% diluted malting effluents for Chlorella sp., whereas the 70% dilution concentration was the most productive for Chlamydomonas (386 × 104 cell·mL−1 on day 16). The total lipid content was higher in the 50% dilution concentration of malting effluent in both Chlorella sp. (maximum 20.5%–minimum 11.5% of dry weight) and Chlamydomonas sp. (max 39.3%–min 25.9% of dry weight). These results emphasize the suitability of using unsterile diluted malting effluent for microalgae cultivation.