Enhanced chloroplast-mitochondria crosstalk promotes ambient algal-H2 production

Microalgae are natural biocatalysts of hydrogen production. Their ability to convert solar energy to valuable compounds with minimal ecological footprint potentially places them as significant contributors to the clean-energy transition. Currently, algal hydrogen production, although promising, is not scalable because it is limited to oxygen-free conditions and is short-lived due to electron loss to other processes, mainly carbon fixation. Here, we show that a strain defective in thylakoid proton gradient regulation, Δpgr5, bypasses both challenges simultaneously, leading to a prolonged 12-day hydrogen production under ambient mixotrophic conditions in a 1-L setup. We report that Δpgr5 possess a repressed ability to fixate carbon and that this limitation is counterbalanced by an enhanced chloroplast-mitochondrion energetic exchange. This unique physiology supports the simplistic, yet robust and scalable, hydrogen production capability of Δpgr5. [Display omitted] •Scalable (from 1-L cultures) algal H2 production over 12 days is demonstrated•Continuous ambient H2 production is possible from Δpgr5 mutant•Δpgr5 bypasses key challenges of H2 production: oxygen accumulation and electron loss•The molecular mechanism behind this phenotype is enhanced mitochondrial biogenesis Hydrogen production from green algae is a fleeting process due to energy loss to competing processes and oxygen accumulation, which inactivate the enzyme catalyzing H2 production. Elman et al. show that a single mutation in green algae bypasses both bottlenecks and allows sustained, scalable H2 production under ambient mixotrophic conditions.