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Medium chain fatty acids (MCFAs) are compounds of considerable commercial interest that have applications in food, feed, and the production of industrially relevant chemicals. Due to their antipathogenic and health-promoting effects, they are further discussed as potential therapeutic agents for disease treatment and infection prevention and control. Domesticated agricultural crops that can grow in temperate climates lack MCFAs, and increased cultivation of tropical MCFA-rich species such as oil palm is associated with deforestation and a decrease in biodiversity. Alternative sources for more sustainably produced MCFAs are non-domesticated plants such as Cuphea spp., as well as oil crops and oleaginous microalgae that can be genetically engineered to accumulate MCFAs by expression of acyl-acyl carrier protein thioesterases (TEs) from MCFA-producing plants. Here, we report the heterologous expression of a TE from Cuphea palustris in the industrially relevant microalga Nannochloropsis oceanica. Using a recently developed gene expression system, we engineered transformant strains that accumulated up to 2.84 and 4.15% of C8:0 and C10:0 in storage lipids, respectively, and we observed no effect on growth. We further show that MCFA accumulation was negatively correlated with total neutral lipid content, suggesting the presence of regulatory mechanisms that limit MCFA accumulation in Nannochloropsis.

Fucoxanthin is a xanthophyll carotenoid with high market value. Currently, seaweeds are the primary source for fucoxanthin industrial production. However, marine microalgae reach 5 to 10 times higher concentrations (2.24 to 26.6 mg g-1 DW) and are considered a promising feedstock. In this work, two marine microalgae were produced at industrial scale to evaluate biomass and fucoxanthin production: Phaeodactylum tricornutum for autumn/winter and Tisochrysis lutea for spring/summer. Both strains were grown in 15 m3 tubular flow-through photobioreactors; for 170 consecutive days of semi-continuous cultivation regime. The average volumetric biomass productivities of P. tricornutum and T. lutea were 0.11 and 0.09 g DW L-1 day-1. P. tricornutum reached higher maximum biomass concentration (2.87 g DW L-1) than T. lutea (1.47 g DW L-1). P. tricornutum fucoxanthin content ranged between 0.2 and 0.7% DW, while T. lutea between 0.2 and 0.6% DW. The fucoxanthin content was correlated with the irradiation (MJ m-2) and biomass concentration in the photobioreactor (g L-1). This is the first work in literature reporting a long-term industrial production of T. lutea. Overall, we showed possible scenarios for fucoxanthin production from microalgae, increasing the window to supply the industry with steady production throughout the year. info:eu-repo/semantics/publishedVersion

In this study the influence of day length on circadian rhythms of N. oleoabundans was investigated. N. oleoabundans was grown in a photobioreactor continuously operated (turbidostat), under various day/night (D/N) cycles; 20D4N, 16D8N and 12D12N. The following variables showed to be regulated by the circadian clock: maximum growth rate, start of starch synthesis and DNA replication to 4 and 8 copies. Timing of these processes was not influenced by day length. The length of the photoperiod caused changes in biomass composition, especially due to variations in starch content. In longer days, more starch was accumulated. Starch was used for cell division probably also when cell division occurred in the light. Therefore, also the timing of cell division should be considered in the production of microalgae biomass. This timing mechanism can be explored to produce biomass with a desired concentration of protein, lipids, carbohydrates or pigments.

The effect of biomass concentration on areal productivity and photosynthetic efficiency of Nannochloropsis sp. CCAP211/78 was studied in three outdoor pilot-scale photobioreactors: an open raceway pond (OPR), a horizontal tubular (HT) photobioreactor and a vertically stacked horizontal tubular (VT) photobioreactor. The reactors were operated continuously as turbidostat at different biomass concentrations. For all systems highest areal productivities were obtained on days with a high light intensity, while the highest photosynthetic efficiencies were obtained on days with a low light intensity. Ground areal biomass concentration exceeding 51 g m − 2 had a negative effect on the areal productivity and photosynthetic efficiency. No significant effect of biomass concentration on the productivity was found for the HT at ground areal biomass concentration lower than 51 g m − 2 . Also for the VT, no significant effect of biomass concentration was found with the exception of the highest biomass concentration of 2.0 g L − 1 (68 g m − 2 ) resulting in decreased productivity. For the open raceway pond the highest biomass concentration (0.5 g L − 1 or 94 g m − 2 ) resulted in significantly lower areal productivity, compared to the lower biomass concentration (0.25 g L 47 g m − 2 ). Highest areal productivities were obtained for OPR and VT, most likely due to more efficient light interception. In this study we observed that night biomass loss was coupled to net growth. At lower biomass concentrations and concomitant higher growth rates the specific biomass loss rate was higher. Microalgal specific light absorption coefficient was correlated to biomass concentration; higher biomass concentrations resulted in higher specific absorption coefficients, resulting in a steeper light gradient in the microalgal cultures.

During the past few years, interest in microalgae has grown, mainly because of their potential for biofuel production. Botryococcus braunii, a green microalga that can accumulate more than half of its dry weight as hydrocarbons, is one of the most important examples. This microorganism grows in colonies and there has been no reliable viability protocol reported for this species as yet. Knowing the number of dead cells in cultures is essential for the development of efficient bioprocesses such as non-destructive extraction procedures (“milking”) to obtain lipid soluble substances from microalgal biomass. Our study presents a simple colorimetric method to determine the proportion of living to dead cells in cultures, based on the uptake of methylene blue in solution by dead B. braunii cells. The main parameters influencing this process were investigated and used to develop a protocol. This technique was validated using flow cytometry and Neochloris oleoabundans, and appears not to be limited to use with B. braunii.

Microalgae gained much interest from industry as promising sustainable feedstock for the production of food, feed, bulk chemicals, and biofuels. Pilot scale research on microalgae is needed to bridge the gap between laboratory scale research and commercial applications. The AlgaePARC (Algae Production And Research Center) pilot facility was constructed to bridge this gap. The objective of this pilot center is to compare and improve photobioreactors and operational strategies under outdoor conditions. The pilot plant facility consists of four production systems (raceway pond, horizontal tubular reactor, vertically stacked tubular reactor and flat panels) and allows comparison of performance of these systems under identical climatological conditions. This paper describes the development of this pilot facility, decisions made during the building process and discusses the production systems including technical specifications, measurements and supporting facilities.

article i nfo The effect of cell cycle stage on biomass composition of the green microalgae Neochloris oleoabundanswas inves- tigated. N. oleoabundans was grown under constant light conditions in a flat panel photobioreactor operated as a turbidostat. Even though light conditions were constant, a synchronized cell division was observed with the cells dividing by multiple fission during the natural night. Presumably, the circadian clock was responsible for 'gating' cell division to this specific time frame. Oscillations in starch, protein and pigment content were observed during the cell cycle. These oscillations could be solely contributed to the cell cycle stage of the synchronized culture, since all experimental conditions were kept constant. A maximum in starch, protein and fatty acid content was obtained just before cell division. Biomass yield was also greatly influenced by the cell cycle and declined to a minimum during cell division. These findings highlight that knowledge of the cell cycle is of importance in microalgae process optimization.

We hypothesized that cells with different diameter have different division rates, which could affect lipid productivity (lipid content × biomass productivity). In the present work we assessed the influence of cell diameter, as a sorting parameter, on both biomass and lipid productivity of Chlorococcum littorale . Prior to sorting, cells were grown in a batch-wise nitrogen run-out including a long nitrogen depleted phase (N −) to stop cell division, thus only having vegetative cells (Pre-sorting). Cell sorting was done at the end of this N − phase using FACS (fluorescence assisted cell sorting) based on forward scatter as a proxy for diameter (size ranges (μm): 5–6 (small), 8–9 (medium), 11–14 (large) and 5–14 (control)). The sorting was done in 2 pools: multiple-cell (100 cells) and single-cell. After sorting, cells were recovered under low-light for 2 weeks, and used to start the Post-sorting experiment (analogous to Pre-sorting). The populations derived from different sorted pools, single-cell and multiple-cell, showed similar size distributions after re-growth. No difference was observed in biomass and lipid productivities among Post-sorting cells and when compared to Pre-sorting cells under nitrogen depletion. We concluded that cellular size had no effect on both biomass and lipid productivity of C. littorale .