H2 production pathways in nutrient-replete mixotrophic Chlamydomonas cultures under low light. Response to the commentary article "On the pathways feeding the H2 production process in nutrient-replete, hypoxic conditions," by Alberto Scoma and Szilvia Z. Tóth

Abstract

Background: A recent Commentary article entitled "On the pathways feeding the H₂ production process in nutrient-replete, hypoxic conditions" by Dr. Scoma and Dr. Tóth, Biotechnology for Biofuels (2017), opened a very interesting debate about the H₂ production photosynthetic-linked pathways occurring in Chlamydomonas cultures grown in acetate-containing media and incubated under hypoxia/anoxia conditions. This Commentary article mainly focused on the results of our previous article "Low oxygen levels contribute to improve photohydrogen production in mixotrophic non-stressed Chlamydomonas cultures," by Jurado-Oller et al., Biotechnology for Biofuels (7, 2015; 8:149).

Main body: Here, we review some previous knowledge about the H₂ production pathways linked to photosynthesis in Chlamydomonas, especially focusing on the role of the PSII-dependent and -independent pathways in acetate-containing nutrient-replete cultures. The potential contributions of these pathways to H₂ production under anoxia/hypoxia are discussed.

Conclusion: Despite the fact that the PSII inhibitor DCMU is broadly used to discern between the two different photosynthetic pathways operating under H₂ production conditions, its use may lead to distinctive conclusions depending on the growth conditions. The different potential sources of reductive power needed for the PSII-independent H₂ production in mixotrophic nutrient-replete cultures are a matter of debate and conclusive evidences are still missing.

Keywords: Acetate; Algae; Biofuels; Biomass; Chlamydomonas; DCMU; Hydrogen; Low light; Oxygen.