Microalgae screening for heterotrophic and mixotrophic growth on butyrate

• Published in: Algal research (Amsterdam) 2022-09, Vol.67, p.102843, Article 102843
• Main Authors: Lacroux, J., Jouannais, P., Atteia, A., Bonnafous, A., Trably, E., Steyer, J.-P., van Lis, R.
• Format: Article
• Language: English
• Subjects: Biotechnology; Carbohydrates; Heterotrophy; Life Sciences; Lipids; Microalgae; Microbiology and Parasitology; Mixotrophy; Volatile fatty acids
• ISSN: 2211-9264; 2211-9264
• DOI: 10.1016/j.algal.2022.102843

Volatile fatty acids (VFAs) produced by fermentative bacteria can be used instead of high value carbohydrates like glucose to reduce the costs associated to mixotrophic microalgal cultivation. This process is however limited by a poor assimilation of butyrate and a low tolerance of microalgae to high VFA concentrations. In this study, 10 microalgae strains, isolated from local natural environments or selected from culture collections were screened for their ability to grow on either acetate or butyrate. The non-photosynthetic Chlorophyte Polytomella sp. was found to be the fastest growing strain on both VFAs, exhibiting a growth rate of 4.0 d−1 on acetate and 2.5 d−1 on butyrate. The tolerance of the different strains to concentrated VFA was further assessed using increasing acid concentrations (1.5–60 g·L−1 for acetate and 1–40 g·L−1 for butyrate). Polytomella sp. appeared as the most resistant, being able to grow up to 38 g·L−1 on acetic acid and to 18 g·L−1 on butyric acid with no inhibitory effect. Finally, biomass yield and productivity, as well as lipid and carbohydrate yields were assessed on a synthetic VFAs mixture (0.8 g·L−1 acetate and 1.2 g·L−1 butyrate) for the most promising strains. Polytomella sp. and Euglena gracilis exhibited the highest carbohydrate yield (respectively 0.65 and 0.58 g·g−1) while lipid yield was maximum for Chlorella sorokiniana (0.42 g·g−1). This work provides new insights in the trophic metabolism of microalgae of highly divergent lineages using VFAs as substrates. •Butyrate but not the acetate in dark fermentation effluents limits microalgae cultivation on effluents.•Ten algal species from peatbogs or culture collections were tested for growth on butyrate and acetate.•Only the heterotrophic alga Polytomella sp. exhibited high growth rates and tolerance to both acids.•Four strains were further cultivated on a synthetic dark fermentation effluent.•Lipids were highest for Chlorella sorokiniana and sugars for Polytomella sp. and Euglena gracilis.