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Faculty Sponsor

Dr. Tanya Soule


Department of Biology

University Affiliation

Indiana University – Purdue University Fort Wayne


UV radiation affects almost all organisms through direct damage to DNA and proteins or indirectly through free radical sensitization. While natural protection from UV in humans comes from the production of the photoprotective pigment melanin, organisms that do not produce melanin have to find alternative strategies. As phototrophic bacteria, cyanobacteria must protect themselves from the UV-B and UV-A radiation from exposure to sunlight. Some cyanobacteria are able to protect themselves through the use of scytonemin, an indole-alkaloid sunscreen that is deposited into the extracellular sheath of the cells that produce it. Nostoc punctiforme ATCC 29133, a scytonemin-producing cyanobacterium, serves as a model organism for understanding scytonemin biosynthesis. While a genomic region that is responsible for scytonemin biosynthesis has been identified, many of the genes within this region remain to be characterized. In particular, it is unknown if the extracellular nature of the sunscreen is coupled to extracellular slime production. Thus, it is necessary to determine if a mutant that lacks the ability to produce scytonemin, SCY 59, is able to produce slime levels comparable to the wild type under the same conditions. Using a wild type strain of N. punctiforme and SCY 59, the relationship between extracellular slime and scytonemin production was investigated using the Phenol-Sulfuric Acid (PSA) test for measuring extractable extracellular carbohydrates. Following the exposure of N. punctiforme and SCY 59 to either white light or white light supplemented with UV-A the amount of extractable carbohydrates was measured. While the carbohydrate production was similar for both strains under white light only and the wild type under UV-A, SCY 59 exposed to UV-A had significantly more slime production. This suggests that scytonemin and extracellular slime production are not coupled and that SCY 59 may be compensating for the lack of scytonemin with excess slime for protection against UV-A radiation.


Biology | Life Sciences

Slime production associated with sunscreen-producing cyanobacteria

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