From: eastside.erik@gmail.com   
      
   Archaean green-light environments drove the evolution of cyanobacteria’s   
   light-harvesting system   
      
   Abstract   
   Cyanobacteria induced the great oxidation event around 2.4 billion years   
   ago, probably triggering the rise in aerobic biodiversity. While   
   chlorophylls are universal pigments used by all phototrophic organisms,   
   cyanobacteria use additional pigments called phycobilins for their   
   light-harvesting antennas—phycobilisomes—to absorb light energy at   
   complementary wavelengths to chlorophylls. Nonetheless, an enigma   
   persists: why did cyanobacteria need phycobilisomes? Here, we   
   demonstrate through numerical simulations that the underwater light   
   spectrum during the Archaean era was probably predominantly green owing   
   to oxidized Fe(III) precipitation. The green-light environments,   
   probably shaped by photosynthetic organisms, may have directed their own   
   photosynthetic evolution. Genetic engineering of extant cyanobacteria,   
   simulating past natural selection, suggests that cyanobacteria that   
   acquired a green-specialized phycobilin called phycoerythrobilin could   
   have flourished under green-light environments. Phylogenetic analyses   
   indicate that the common ancestor of modern cyanobacteria embraced all   
   key components of phycobilisomes to establish an intricate energy   
   transfer mechanism towards chlorophylls using green light and thus   
   gained strong selective advantage under green-light conditions. Our   
   findings highlight the co-evolutionary relationship between oxygenic   
   phototrophs and light environments that defined the aquatic landscape of   
   the Archaean Earth and envision the green colour as a sign of the   
   distinct evolutionary stage of inhabited planets.   
      
   https://www.nature.com/articles/s41559-025-02637-3 (Open access)   
      
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