Effect of plant growth-promoting molecules on improving biomass productivity in DISCOVR production strains

Phytohormones (Growth-Promoting Molecules, GPMs) have specific functions in the life cycle of a plant and are known to regulate plant growth, development, and stress responses independently, as well as through crosstalk with each other. These phytohormones are actively used in agriculture at scale, due to their efficiency at very low concentrations, and they also can be cost effective. Two phytohormones, auxin (indole-3-acetic acid, IAA) and gibberellic acid (GA), have also been shown to improve cell division, growth, and biomass production in algae. To test if phytohormones might have a similar beneficial result on potential algae biomass production strains, we evaluated the effect of IAA and GA3 on top-performing algae DISCOVR strains, Chlorella sorokiniana 1412, Monoraphidium minutum 26B-AM, Picochlorum celeri TG2-WT-CSM/EMRE, and Tetraselmis striata LANL1001 under laboratory conditions. Both GPMs showed growth promoting effects, but in contrast to previously published studies, we did not observe any increase in lipid accumulation with either IAA or GA3 supplementation. Then, to test phytohormone effects in a simulated outdoor environment, IAA treatments were conducted in environmental photobioreactors, revealing that IAA treatment significantly increased the growth and total biomass of M. minutum 26B-AM. In addition, investigation of the M. minutum 26B-AM genome combined with transcriptome data analysis revealed the presence of genes putatively involved in auxin biosynthesis and signaling, demonstrating that IAA pathways found in other algal species are also present in M. minutum 26B-AM. Finally, to begin to gauge whether GPM treatment is a viable approach for increasing biomass productivity in outdoor cultivation, we assessed, for the first time, the effects of adding GPMs to algae during scaled cultivation and the associated implications on economics for modeled large-scale algae farms.