Previously unrecognized diversity of far-red light-using terrestrial green algae and cyanobacteria

Oxygenic photosynthesis in cyanobacteria, algae, and plants typically relies on visible light, but some lineages can utilize far-red light (FRL, wavelength = 700–800 nm). While FRL-utilizing cyanobacteria are well-studied, little is known about FRL-utilizing algae. Here, we isolated ten algal and three cyanobacterial strains capable of growing under FRL from soil, brick surface, and bark in a Taiwan urban park. Ten isolates belong to four green algal genera not previously reported to use FRL. These algae showed distinct far-red absorption and enhanced long-wavelength fluorescence compared to a model green alga. Unlike cyanobacteria producing chlorophylls d and f, these algae contain only chlorophylls a or b, suggesting red-shifted chlorophyll a in their light-harvesting complexes. Phylogenetic analysis showed these algae are not distinct lineages but cluster with known genera, suggesting that their ability to grow in FRL had been previously overlooked due to the lack of functional screening.