Simultaneous control of turbidity and dilution rate through adjustment of medium composition in semi-continuousChlamydomonas cultures

Enhanced growth and metabolite production from a novel strain of Porphyridium sp

Microalgae are capable of generating numerous metabolites that possess notable biological activities and hold substantial promise for various industrial applications. Nevertheless, the taxonomic diversity of these photosynthetic microorganisms has not received thorough investigation. Using the 18S rRNA encoding gene, a recently discovered strain originating from the Tunisian coast (the governorate of Mahdia) was identified as a member of the Porphyridium genus. The growth response as well as the metabolite accumulation of Porphyridium sp. to different culture media (Pm, F/2, and Hemerick) was investigated over a period of 52 days. The highest biomass production was recorded with Pm medium (2 × 107 cell/mL). The apparent growth rates (µ) and the doubling time (Dt) were about 0.081 day-1 and 12.34 days, respectively. The highest chlorophyll a (0.678 ± 0.005 pg/cell), total carotenoids (0.18 ± 0.003 pg/cell), phycoerythrin (3.88 ± 0.003 pg/cell), and proteins (14.58 ± 0.35 pg/cell) contents were observed with F/2 medium. Cultivating Porphyridium sp. in both F/2 and Hemerick media yielded similar levels of starch accumulation. The Hemerick medium has proven to be the most suitable for the production of lipids (2.23% DW) and exopolysaccharides (5.41 ± 0.56 pg/cell).

Nutritional optimization of Arthrospira platensis for starch and Total carbohydrates production

Present study aims to optimize the production of starch and total carbohydrates from Arthrospira platensis. Growing concerns toward unprecedented environmental issues associated with plastic pollution has created a tremendous impetus to develop new biomaterials for the production of bioplastic. Starch-based biopolymers from algae serve as sustainable feedstock for thermoplastic starch production due to their abundant availability and low cost. A. platensis was cultivated in Zarrouk's medium at 32 ± 1°C and exposed to red light with a photoperiod of 12:12 hr light/dark. Growth kinetics studies showed that the maximum specific growth rate (μ_max ) obtained was 0.059 day^-1 with the doubling time (t_d ) of 11.748 days. Subsequently, Zarrouk's medium with different concentrations of sulfur, phosphorus and nitrogen was prepared to establish the nutrient-limiting conditions to enhance the accumulation of starch and total carbohydrates. In this study, the highest starch accumulated was 6.406 ± 0.622 mg L^-1 under optimized phosphorus limitation (0.025 g L^-1 ) conditions. Nitrogen limitation (0.250 g L^-1 ) results demonstrated significant influenced (p < 0.05) on total carbohydrates (67.573 ± 2.893 mg L^-1 ) accumulation in A. platensis. The starch accumulation in A. platensis was significantly affected (p < 0.05) by phosphorus limitation (0.0025 g L^-1 ). Subsequently, the optimized phosphorus concentration was coupled with mixotrophic cultivation to further enhance the starch accumulation. The results obtained indicated that, the starch (11.426 ± 0.314 mg L^-1 ) and carbohydrates (43.053 ± 2.986 mg L^-1 ) concentration obtained was significantly high (p < 0.05) under mixotrophic cultivation. Therefore, it shown that nutrient limitation and mixotrophic cultivation are viable strategies to enhance the accumulation of starch and total carbohydrates in A. platensis.

Maximizing the productivity of the microalgae Scenedesmus AMDD cultivated in a continuous photobioreactor using an online flow rate control

In this study, production of the microalga Scenedesmus AMDD in a 300 L continuous flow photobioreactor was maximized using an online flow (dilution rate) control algorithm. To enable online control, biomass concentration was estimated in real time by measuring chlorophyll-related culture fluorescence. A simple microalgae growth model was developed and used to solve the optimization problem aimed at maximizing the photobioreactor productivity. When optimally controlled, Scenedesmus AMDD culture demonstrated an average volumetric biomass productivity of 0.11 g L^-1 d^-1 over a 25 day cultivation period, equivalent to a 70 % performance improvement compared to the same photobioreactor operated as a turbidostat. The proposed approach for optimizing photobioreactor flow can be adapted to a broad range of microalgae cultivation systems.

Photobioreactors in Life Support Systems

Life support systems for long-term space missions or extraterrestrial installations have to fulfill major functions such as purification of water and regeneration of atmosphere as well as the generation of food and energy. For almost 60 years ideas for biological life support systems have been collected and various concepts have been developed and tested. Microalgae as photosynthetic organisms have played a major role in most of these concepts. This review deals with the potentials of using eukaryotic microalgae for life support systems and highlights special requirements and frame conditions for designing space photobioreactors especially regarding illumination and aeration. Mono- and dichromatic illumination based on LEDs is a promising alternative for conventional systems and preliminary results yielded higher photoconversion efficiencies (PCE) for dichromatic red/blue illumination than white illumination. Aeration for microgravity conditions should be realized in a bubble-free manner, for example, via membranes. Finally, a novel photobioreactor concept for space application is introduced being parameterized and tested with the microalga Chlamydomonas reinhardtii. This system has already been tested during two parabolic flight campaigns.