Commercial production of eicosapentaenoic acid (EPA) from photoautotrophic microalgae like Nannochloropsis oceanica requires higher productivity and larger scales to reduce costs. Improving productivity can be achieved by increasing biomass concentrations, which creates light gradients in the reactor depending on the culture’s acclimation and the reactor geometry. These light gradients affect physiology, lipid synthesis, but also the distribution of fatty acids between lipid classes. In this study we evaluated the combined effect of the incident light intensity and light gradient on growth, biochemical composition, and fatty acid distribution between lipid classes. A total of 13 cultivations were performed in continuous mode using three different incident light intensities (200, 670, and 1550 μmol photons m−2 s−1) and four dilution rates (from 0.29 to 0.75 day−1). Reducing dilution rates resulted in higher biomass concentrations, steeper light gradients, and lower average light intensities. Increasing incident light intensity improved biomass productivity from 0.5 to 1.8 g L−1 day−1, while the biomass yield on light decreased from 1.05 to 0.44 g mol−1. Lowering average light intensities decreased the triglyceride content from 11.1 to 1.5

Biotechnology and BioengineeringVolume 120, Issue 6 p. 1451-1454 ISSUE INFORMATIONFree Access Biotechnology and Bioengineering: Volume 120, Number 6, June 2023 First published: 12 May 2023 https://doi.org/10.1002/bit.28139AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Volume120, Issue6June 2023Pages 1451-1454 RelatedInformation

Oxygen-balanced mixotrophy (OBM) is a novel type of microalgal cultivation that improves autotrophic productivity while reducing aeration costs and achieving high biomass yields on substrate. The scale-up of this process is not straightforward, as nonideal mixing in large photobioreactors might have unwanted effects in cell physiology. We simulated at lab scale dissolved oxygen and glucose fluctuations in a tubular photobioreactor operated under OBM where glucose is injected at the beginning of the tubular section. We ran repeated batch experiments with the strain Galdieria sulphuraria ACUF 064 under glucose pulse feeding of different lengths, representing different retention times: 112, 71, and 21 min. During the long and medium tube retention time simulations, dissolved oxygen was depleted 15-25 min after every glucose pulse. These periods of oxygen limitation resulted in the accumulation of coproporphyrin III in the supernatant, an indication of disruption in the chlorophyll synthesis pathway. Accordingly, the absorption cross-section of the cultures decreased steeply, going from values of 150-180 m(2) kg(-1) at the end of the first batch down to 50-70 m(2) kg(-1) in the last batches of both conditions. In the short tube retention time simulation, dissolved oxygen always stayed above 10% air saturation and no pigment reduction nor coproporphyrin III accumulation were observed. Concerning glucose utilization efficiency, glucose pulse feeding caused a reduction of biomass yield on substrate in the range of 4%-22% compared to the maximum levels previously obtained with continuous glucose feeding (0.9 C-g C-g(-1)). The missing carbon was excreted to the supernatant as extracellular polymeric substances constituted by carbohydrates and proteins. Overall, the results point out the importance of studying large-scale conditions in a controlled environment and the need for a highly controlled glucose feeding strategy in the scale-up of mixotrophic cultivation.

Regions that offer high levels of sunlight are ideal to produce microalgae. However, as a result of high light intensities, the temperature in photobioreactors can reach temperatures up to 50 degrees C. Control of temperature is essential to avoid losses on biomass productivity but should be limited to a minimum to avoid high energy requirements for cooling. Our objective is to develop a production process in which cooling is not required. We studied the behaviour of thermotolerant microalgae Picochlorum sp. (BPE23) under four diel temperature regimes, with peak temperatures from 30 degrees C up to a maximum of 47.5 degrees C. The highest growth rate of 0.17 h-1 was obtained when applying a daytime peak temperature of 40 degrees C. Operating photobioreactors in tropical regions, with a maximal peak temperature of 40 degrees C, up from 30 degrees C, reduces microalgae production costs by 26.2 %, based on simulations with a pre-existing techno-economic model. Cell pigmentation was downregulated under increasingly stressful temperatures. The fatty acid composition of cell membranes was altered under increasing temperatures to contain shorter fatty acids with a higher level of saturation. Our findings show that the level of temperature control impacts the biomass yield and composition of the microalgae.

Vaccines pave the way out of the SARS-CoV-2 pandemic. We have developed a virus-like particle (VLP)-based vaccine using the baculovirus-insect cell expression system, a robust production platform known for its scalability, low cost, and safety. Baculoviruses were constructed encoding SARS-CoV-2 spike proteins: full-length S, stabilized secreted S, or the S1 domain. This two-component nanoparticle vaccine can now be further developed to help alleviate the burden of COVID-19.

A method to determine the content and composition of total fatty acids present in microalgae is described. Fatty acids are a major constituent of microalgal biomass. These fatty acids can be present in different acyl-lipid classes. Especially the fatty acids present in triacylglycerol (TAG) are of commercial interest, because they can be used for production of transportation fuels, bulk chemicals, nutraceuticals (ω-3 fatty acids), and food commodities. To develop commercial applications, reliable analytical methods for quantification of fatty acid content and composition are needed. Microalgae are single cells surrounded by a rigid cell wall. A fatty acid analysis method should provide sufficient cell disruption to liberate all acyl lipids and the extraction procedure used should be able to extract all acyl lipid classes. With the method presented here all fatty acids present in microalgae can be accurately and reproducibly identified and quantified using small amounts of sample (5 mg) independent of their chain length, degree of unsaturation, or the lipid class they are part of. This method does not provide information about the relative abundance of different lipid classes, but can be extended to separate lipid classes from each other. The method is based on a sequence of mechanical cell disruption, solvent based lipid extraction, transesterification of fatty acids to fatty acid methyl esters (FAMEs), and quantification and identification of FAMEs using gas chromatography (GC-FID). A TAG internal standard (tripentadecanoin) is added prior to the analytical procedure to correct for losses during extraction and incomplete transesterification.