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

This upload provides all the data and code associated with the manuscript "Hunting for extremophiles: a systematic screening of freshwater microalgae for tolerance to high pH and high alkalinity cultivation" in ACS Sustainable Chemistry & Engineering under the DOI: https://doi.org/10.1021/acssuschemeng.5c09906 Data should be analyzed in R or R studio. The code in the .Rmd file should execute automatically with no modifications by the user as long as the csv file containing data "growth_over_time.csv" is placed in the same working directory that R is set to. The R project (.Rproj) file may also be opened directly to create an R project that is automatically set to the correct directory; again, all files should be placed in one folder for this to work. Metadata explaining the contents of the data file is provided in the README.csv file. Additionally, one html file is provided which contains all the code and output in R markdown format; this allows users to view code and output without directly running code in R. 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 inhibited 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.