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bioRxiv · 10.1101/2025.09.15.676395

Hunting for extremophiles: a systematic screening of freshwater microalgae for tolerance to high pH and high alkalinity cultivation

Thomas, P. K.·Gerlach, R.·Narwani, A.
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Abstract

Microalgae hold the potential to supply sustainable food, fuel, plastics, and chemicals at commercial scales. Cultivating microalgae at extreme pH (>10) and high alkalinity provides multiple benefits including 1) reducing the risk of contamination by undesired organisms and 2) enabling direct air capture of CO2, which expands the land area suitable for algae farming compared to using CO2 point sources alone. However, we currently have a limited understanding of which algal taxa can grow under these conditions. Therefore, we conducted a high-throughput screening of 49 freshwater microalgae strains, comprising 40 species, for their ability to grow in moderate (pH 8.5, 25 mM alkalinity), high (pH 10, 75 mM alkalinity), and extreme (pH 10, 150 mM alkalinity) cultivation environments. Our results show that moderate alkalinity tends to significantly increase algae growth (including potentially harmful strains). However, higher levels inhibit all but a small subset of green algae and cyanobacteria. Effects of salinity and alkalinity differed, indicating they are broadly decoupled. Our results identify new industrially relevant alkaline-tolerant strains, show that algae isolated from "normal" ecosystems can be extremophilic, and suggest that future bioprospecting efforts for alkaline-tolerant algae adapted to local climatic conditions could yield additional productivity gains for the algae industry. SynopsisWe tested if 49 distinct microalgae strains could grow in high pH environments and found new and productive alkaline-tolerant strains Abstract/TOC Graphic O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/676395v1_ufig1.gif" ALT="Figure 1"> View larger version (73K): org.highwire.dtl.DTLVardef@63d59dorg.highwire.dtl.DTLVardef@5d597eorg.highwire.dtl.DTLVardef@9e9be7org.highwire.dtl.DTLVardef@10d9160_HPS_FORMAT_FIGEXP M_FIG C_FIG

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Thomas, P. K., Gerlach, R., Narwani, A.. 2025-09-15. Hunting for extremophiles: a systematic screening of freshwater microalgae for tolerance to high pH and high alkalinity cultivation. https://doi.org/10.1101/2025.09.15.676395

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