Competition for light color between marine Synechococcus strains with fixed and variable pigmentation

Area of Science:

• Marine microbiology
• Phytoplankton ecology
• Photosynthetic pigment evolution

Background:

• Phytoplankton species diversification is driven by light competition, leading to varied photosynthetic pigments.
• Synechococcus cyanobacteria exhibit three pigment types: blue light (BL) specialists, green light (GL) specialists, and chromatic acclimaters (CA4).

Purpose of the Study:

• To test the hypothesis that chromatic acclimation (CA4) confers a fitness advantage in specific light conditions.
• To understand the competitive dynamics between different Synechococcus pigment types under varying light spectra and intensities.

Main Methods:

• Monocultures and co-cultures of BL specialist, GL specialist, and CA4-capable Synechococcus strains were performed in chemostats.
• A resource competition model was parameterized using monoculture data to predict co-culture outcomes.
• Competition experiments were conducted under different light color and intensity conditions.

Main Results:

• Model predictions aligned with experimental results: BL specialists dominated low blue light, and GL specialists dominated low and high green light.
• CA4-capable strains were disadvantaged at low light but outcompeted specialists in high blue light conditions.
• Different pigment types occupy distinct spectral niches, with CA4 providing a competitive edge in high blue light environments.

Conclusions:

• Chromatic acclimation in Synechococcus allows adaptation to specific light environments, particularly high blue light.
• The competitive success of different pigment types is strongly dependent on light availability and spectral quality.
• This study elucidates niche partitioning strategies employed by marine phytoplankton for survival and dominance in diverse oceanic light fields.