Multiple Photolyases Protect the Marine Cyanobacterium Synechococcus from Ultraviolet Radiation

Area of Science:

• Marine microbiology
• Molecular biology
• Genetics

Background:

• Marine cyanobacteria inhabit the photic zone, exposed to harmful UV radiation (UVR).
• Photoprotection mechanisms, including DNA repair enzymes like photolyases, are vital for cyanobacterial survival but remain incompletely understood.
• Photolyases are light-activated enzymes that repair UV-induced DNA dimers.

Purpose of the Study:

• To investigate the diversity and function of photolyase/cryptochrome family genes in marine cyanobacteria.
• To determine the role of these photolyases in UV radiation resistance in *Synechococcus*.

Main Methods:

• Comparative genomics of 81 marine cyanobacterial strains (*Synechococcus*, *Cyanobium*, *Prochlorococcus*).
• Gene disruption via genetic manipulation in *Synechococcus* sp. strain RS9916.
• Functional analysis by transforming genes into *Escherichia coli* lacking its own DNA repair mechanisms.

Main Results:

• Marine cyanobacteria possess up to five photolyase/cryptochrome genes, including a novel structural variant.
• Disruption of individual photolyase genes in *Synechococcus* reduced UV radiation survival.
• Transformed photolyase genes enhanced UV radiation tolerance in *E. coli*.

Conclusions:

• Marine cyanobacteria possess an extensive set of photolyases contributing significantly to their UV radiation tolerance.
• These photolyases provide a much greater level of UV radiation resistance in *Synechococcus* compared to *E. coli*.
• The study reveals a previously undescribed structural class of DNA photolyases.