Photosynthetic Energy Transfer Mechanisms in Cyanobacterial Systems

Cyanobacteria harness solar energy through highly organised pigment–protein complexes that channel excitation energy to photosynthetic reaction centres. Two principal pathways coexist: chlorophyll-based light harvesting within the thylakoid membrane and phycobiliprotein antenna systems that absorb complementary wavelengths. Phycobilisomes form supramolecular assemblies of phycocyanin and allophycocyanin which funnel excitons towards photosystem II and photosystem I. Variations in complex architecture—from the canonical hemidiscoidal “rod and core” arrangement to ancestral paddle-shaped scaffolds—demonstrate evolutionary optimisations in absorption efficiency and spectral coverage. Under far-red illumination, specialised mechanisms such as far-red light photoacclimation (FaRLiP) introduce modified chlorophylls (notably chlorophyll f) and paralogous photosystem subunits, extending functional absorption beyond 700 nm. Structural adaptations of antenna proteins, including helical allophycocyanin nanotubes and peripheral binding of red-shifted chlorophylls in photosystem I, illustrate the balance between maximising light harvesting in niche environments and maintaining rapid energy transfer rates. Understanding these mechanisms underpins advances in bioengineering of solar-energy capture and illuminates the global ecological success of cyanobacteria across diverse light regimes.

Research from Nature Portfolio

Recent work has elucidated an ancestral form of the phycobilisome from a thylakoid-free cyanobacterium, revealing a paddle-shaped complex lacking peripheral rods and specialised linkers. Cryo-electron microscopy and ultrafast spectroscopy showed that this relict antenna absorbs light over an extended interface but transfers energy less efficiently than modern rod-based assemblies, suggesting an early evolutionary trade-off between absorption breadth and transfer speed. Another study resolved high-resolution structures of photosystem I from a chlorophyll f-containing cyanobacterium grown under white or far-red light. Seven chlorophyll f molecules were found at peripheral sites of the reaction centre, where they harvest far-red photons and facilitate uphill energy transfer into the core. These findings highlight how gene-encoded modifications and pigment diversification integrate to expand the usable solar spectrum.

Photosynthetic Energy Transfer Mechanisms in Cyanobacterial Systems publication trend

The graph below shows the total number of articles in photosynthetic energy transfer mechanisms in cyanobacterial systems across all publications each year (not limited to Nature Index journals).

Technical terms

Phycobilisome: A large water-soluble antenna complex composed of phycobiliprotein rods and core subunits that captures and funnels light energy to photosystems.

Exciton: A bound state of an excited electron and its associated hole that migrates between pigments during energy transfer.

Far-red light photoacclimation (FaRLiP): A regulatory response in certain cyanobacteria that remodels photosynthetic complexes and introduces red-shifted pigments to absorb wavelengths beyond 700 nm.

Chlorophyll f: A naturally occurring chlorophyll derivative with an absorption peak in the far-red region, incorporated into photosystem complexes under specific light conditions.

Photosystem I (PSI): A membrane-embedded pigment–protein complex that uses excitation energy to drive electron transfer and ultimately reduce ferredoxin in oxygenic photosynthesis.

References

1. A structure of the relict phycobilisome from a thylakoid-free cyanobacterium. Nature Communications (2023).
2. Helical allophycocyanin nanotubes absorb far-red light in a thermophilic cyanobacterium. Science Advances (2023).
3. The structure of Photosystem I acclimated to far-red light illuminates an ecologically important acclimation process in photosynthesis. Science Advances (2020).