Marine Synechococcus picocyanobacteria: Light utilization across latitudes

Area of Science:

• Marine microbiology
• Evolutionary biology
• Photosynthesis research

Background:

• Synechococcus, a ubiquitous marine cyanobacterium, exhibits diverse temperature ecotypes.
• Understanding how these ecotypes adapt light utilization to thermal niches is key to predicting ocean productivity.

Purpose of the Study:

• To investigate the evolution of light utilization in Synechococcus ecotypes across different temperature ranges.
• To determine the role of temperature in the adaptation of photosynthetic machinery and photoprotection.

Main Methods:

• Comparative growth experiments across temperature gradients using tropical (clade II) and subpolar (clade I) Synechococcus strains.
• Analysis of photosynthetic machinery components, photosystem cross-section, and electron flux.
• Metagenomic and bioinformatic analyses of orange carotenoid protein (OCP) gene prevalence and OCP variant evolution.

Main Results:

• Tropical Synechococcus (clade II) thrives at >25 °C with enhanced photosynthesis but fails below 16 °C.
• Subpolar Synechococcus (clade I) grows slower but survives below 10 °C, utilizing increased orange carotenoid protein (OCP) for photoprotection.
• OCP gene prevalence is highest in cold niches; OCP variants in cold-adapted clades show convergent evolution in molecular flexibility.

Conclusions:

• Temperature significantly drives the evolution of OCP and light utilization strategies in Synechococcus.
• Metabolic costs of these adaptations impact Synechococcus competitiveness in a warming ocean.
• Findings inform models predicting ocean carbon flux changes under global warming.