Solar ultra violet radiation or UVR (wavelengths shorter than 400 nm) is associated with biological deleterious effects in living organisms. Among these, some cyanobacteria must thrive in habitats exposed to high doses of UVR such as soil and rock surfaces, and thus have the ability to synthesize and accumulate UV-sunscreens. Sunscreens serve as passive preventative mechanisms that allow the organism to stop UVR before it reaches the cellular machinery, DNA, or produces reactive oxygen species.

The indole-alkaloid, scytonemin, found exclusively among cyanobacteria, is one such sunscreen. It is a brownish-yellow, lipid-soluble pigment located in the extracellular matrix of the cells. The production of scytonemin is induced by UV-A (315-400 nm) and the conjugated double-bond distribution allows for the molecule to absorb strongly in that range (with a maximum of ~384 nm). Scytonemin also has potential in biomedical applications because of its strong anti-proliferative and anti-inflammatory activity.

Another class of sunscreens found in cyanobacteria are the mycosporine-like amino acids (MAAs), water soluble, colorless products that absorb and are induced by UV-B (280-315 nm).

Our lab is currently focusing on the molecular genetics of scytonemin and MAAs biosynthesis.

The model organism that we use to study sunscreen biosynthesis is the filamentous heterocystous cyanobacterium Nostoc punctiforme ATCC 29133/PCC 73102 (from the order Nostocales).
N. punctiforme was originally isolated from the symbiotic association with the gymnosperm cycad Macrozamia sp. and it is one of the few cyanobacteria that can grow heterotrophically. In addition, the fact that N. punctiforme is amenable to genetic manipulation (by electroporation or conjugation) and its genome is fully sequenced (US Department of Energy’s Joint Genome Institute (JGI) database), make it a good model for our work.

Using N. punctiforme, we have been able to obtain a scytonemin-deficient mutant by random transposon insertion into a putative gene. The genomic region of mutation has been identified and is currently being studied for its significance in the biosynthesis of scytonemin, as well as its presence in other scytonemin-producing cyanobacteria.