Hydrogen Production by a Chlamydomonas reinhardtii Strain with Inducible Expression of Photosystem II.

Khorcheska Batyrova,Patrick C Hallenbeck

doi:10.3390/ijms18030647

Abstract

Chlamydomonas reinhardtii cy6Nac2.49 is a genetically modified algal strain that activates photosynthesis in a cyclical manner, so that photosynthesis is not active constitutively in the presence of oxygen, but is turned on only in response to a metabolic trigger (anaerobiosis). Here, we further investigated hydrogen production by this strain comparing it with the parental wild-type strain under photoheterotrophic conditions in regular tris-acetate-phosphate (TAP) medium with a 10-h:14-h light/dark regime. Unlike the wild-type, whose level of H2 production remained low during illumination, H2 production in the mutant strain increased gradually with each subsequent light period, and by the final light period was significantly higher than the wild-type. The relatively low Photosystem II (PSII) activity of the mutant culture was shown by low fluorescence yield both in the dark (Fv/Fm) and in the light (δF/Fm’) periods. Measurement of oxygen evolution confirmed the low photosynthetic activity of the mutant cells, which gradually accumulated O2 to a lesser extent than the wild-type, thus allowing the mutant strain to maintain hydrogenase activity over a longer time period and to gradually accumulate H2 during periods of illumination. Therefore, controllable expression of PSII can be used to increase hydrogen production under nutrient replete conditions, thus avoiding many of the limitations associated with nutrient deprivation approaches sometimes used to promote hydrogen production.

Highlights

The ability of green algae to produce hydrogen in the light was discovered nearly 75 years ago by Gaffron and Rubin, 1942 [1]
Chlamydomonas reinhardtii (C. reinhardtii) uses light for input energy and CO2 as a feedstock to oxidize water to produce organic carbon compounds and nicotinamide adenine dinucleotide phosphate (NADPH) for energy. This creates a paradox for the production of biohydrogen from C. reinhardtii since photosynthesis provides the building blocks for hydrogen gas production and generates oxygen, an inhibitor of hydrogen gas production
In order to produce biological hydrogen using C. reinhardtii, specific strategies are required that separate photosynthesis and hydrogen production in time and/or space

Summary

Introduction

The ability of green algae to produce hydrogen in the light was discovered nearly 75 years ago by Gaffron and Rubin, 1942 [1]. Chlamydomonas reinhardtii (C. reinhardtii) uses light for input energy and CO2 as a feedstock to oxidize water to produce organic carbon compounds and nicotinamide adenine dinucleotide phosphate (NADPH) for energy This creates a paradox for the production of biohydrogen from C. reinhardtii since photosynthesis provides the building blocks for hydrogen gas production (protons and electrons) and generates oxygen, an inhibitor of hydrogen gas production. Photosynthesis does not occur and the residual dissolved oxygen present in the surrounding aqueous environment is consumed by mitochondrial respiration [3] This leads to the transcription and translation of the hydrogenase enzyme, which when active, produces hydrogen for only a brief moment in response to light until oxygen is produced to inhibitory concentrations. In order to produce biological hydrogen using C. reinhardtii, specific strategies are required that separate photosynthesis and hydrogen production in time and/or space

Methods

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Discussion

Conclusion