Exceptional Quantum Efficiency Powers Biomass Production in Halotolerant Algae Picochlorum sp.

Area of Science:

• Photosynthesis research
• Algal biotechnology
• Molecular biology

Background:

• The green algal genus Picochlorum is recognized for its resilience to environmental stressors.
• Understanding the mechanisms behind its robust photosynthetic activity is crucial for biotechnological applications.

Purpose of the Study:

• To compare the metabolic and photosystem II (PSII) performance of Picochlorum SE3 and P. oklahomense against other phototrophs.
• To elucidate the factors contributing to the exceptional light energy conversion efficiency in Picochlorum species.

Main Methods:

• Comparative analysis of metabolic performance in Picochlorum SE3 and P. oklahomense.
• Quantification of quantum yield (QY) for O2 evolution normalized to PSII subunit PsbA (D1) protein and active PSII.
• Investigation of factors influencing electron transfer rates, including water oxidizing complex (WOC) efficiency and plastoquinol reoxidation.

Main Results:

• Picochlorum species demonstrated the highest observed QY for O2 evolution among phototrophs.
• Efficient water oxidizing complex (WOC) and rapid reoxidation of plastoquinol (PQH2) by Cyt b6f/PETC contribute to high electron flux.
• Distinct PSII centers, potentially specialized for linear and cyclic electron flow, were suggested, with unique D1 protein features resembling cyanobacterial isoforms.

Conclusions:

• Picochlorum exhibits a unique, highly efficient PSII mechanism for light energy conversion, surpassing other known phototrophs.
• The observed performance is attributed to an efficient WOC, rapid PQH2 reoxidation, and potentially distinct PSII center types.
• Specific amino acid variations in the D1 protein may enhance water oxidation and electron/proton flux, contributing to high-light performance.