Gabrielsen, T. M. | Search bioRxiv

bioRxiv2025

Biomass Production, Phosphorus Use Efficiency, and Fatty Acid Composition in Phaeodactylum tricornutum Cultivated in Wastewater from an Atlantic Salmon Recirculating Aquaculture System

Recirculating Aquaculture Systems (RAS) are becoming increasingly important as a sustainable method for fish production. However, further advancements are needed to enhance the sustainability of RAS, particularly in the management of waste-streams. Furthermore, the capital and operational expenditures of running a RAS is high, so solutions turning waste-streams into added value is a focus area for the industry moving forward. Wastewater is high in nitrogen, and phosphorus (P) is foreseen to be the limiting nutrient. Here we evaluated the growth dynamics, biomass production, nutrient uptake, phosphorus use efficiency (PUE), and fatty acid composition of the diatom Phaeodactylum tricornutum cultivated in aquaculture wastewater (AWW) from a land-based Atlantic salmon RAS. The diatom was cultivated in various treatments at pilot scale (10 L), including 100% AWW and AWW supplemented with silicon (Si) and P, and compared with a control treatment using Guillards F/2 medium. The highest dry weight biomass concentrations of [~]2.0 g L-{superscript 1} was achieved for the nutrient-supplemented AWW treatments, even outcompeting the control, demonstrating its viability as a growth medium when supplemented with Si and P. The control treatment achieved the highest specific growth rate of 0.422 d-{superscript 1}. The "Si+P addition" treatment achieved the highest PUE, indicating that co-supplementation strategies can enhance phosphorus utilization. However, fatty acid yields, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), were lower in AWW-based treatments, likely due to micronutrient deficiencies or the effect of possible contaminants. Despite this, P. tricornutum cultivated in AWW offers a sustainable and possible cost-effective solution for producing biomass and valuable fatty acids.

plant biology↗

bioRxiv2021

Linking extreme seasonality and gene expression in arctic marine protists

At high latitudes, strong seasonal differences in light availability affect marine organisms and restrict the timing of ecosystem processes. Marine protists are key players in Arctic aquatic ecosystems, yet little is known about their ecological roles over yearly cycles. This is especially true for the dark polar night period, which up until recently was assumed to be devoid of biological activity. A 12 million transcripts catalogue was built from 0.45-10 m protist assemblages sampled over 13 months in a time series station in an arctic fjord in Svalbard. Community gene expression was correlated with seasonality, with light as the main driving factor. Transcript diversity and evenness were higher during polar night compared to polar day. Light-dependent functions had higher relative expression during polar day, except phototransduction. 64% of the most expressed genes could not be functionally annotated, yet up to 78% were identified in arctic samples from Tara Oceans, suggesting that arctic marine assemblages are distinct from those from other oceans. Our study increases understanding of the links between extreme seasonality and biological processes in pico- and nanoplanktonic protists. Our results set the ground for future monitoring studies investigating the seasonal impact of climate change on the communities of microbial eukaryotes in the High Arctic.

microbiology↗