Green light suppresses cell growth but enhances photosynthetic rate and MIB biosynthesis in PE-containing Pseudanabaena

2-Methylisoborneol (MIB) is a notorious musty odorant in drinking water systems, produced by cyanobacteria during the biosynthesis of photosynthetic pigments. This study investigated the physiological adaptation of Pseudanabaena cinerea, a phycoerythrin (PE)-containing and MIB-producing cyanobacterium, by inducing chromatic acclimation under different light color. Our findings revealed that red light enhanced growth rates by stimulating the tricarboxylic acid (TCA) cycle and associated metabolic processes, while green light significantly increased photosynthetic pigment content and electron transport efficiency. MIB yield correlated nonlinearly with chlorophyll a (Chl a) content, modeled by a logarithmic-linear equation (R² = 0.74, p < 0.01). This was supported by the strong correlation between mic and chlG gene expression at the RNA level (R² = 0.85, p < 0.01). The model showed that < 2 % of carbon flux is allocated to MIB biosynthesis compared to Chl a production, indicating that MIB biosynthesis is synergistic, not competitive, with photosynthetic pigment production. The red-shift in light spectra due to increased water turbidity observed in the field led to changes in photosynthetic pigments, which decreased MIB levels. This study improves our understanding of MIB-producing cyanobacteria under variable light conditions and offers insights for mitigating MIB occurrences in surface waters.