The Role of Scytonemin in the Adaptation to Oxidative Stress in Cyanobacteria

Cyanobacteria are photosynthesizing organisms that live in environments open to solar ultraviolet radiation. In order to survive in these environments, some cyanobacteria produce sunscreen pigments. For these organisms, sunscreen pigments such as scytonemin intercept photons before they can harm cellular machinery, DNA, or produce reactive oxygen species (ROS), which are toxic to the cells. The specific aims of this project were to determine how the presence of scytonemin in the cyanobacterium Nostoc punctiforme contributes to fitness under oxidative stress and to provide insight into the molecular response to oxidative stress with and without the protection of scytonemin. To assess the physiological response, cells were first induced to produce scytonemin with long-wavelength UVA radiation. Then they were stressed with methylene blue for 30 min to induce production of ROS and evaluated for antioxidant enzyme activity. A control group without scytonemin and methylene blue stress were similarly evaluated. The gene expression response to oxidative stress was also measured with quantitative-PCR (qPCR) by targeting basic metabolic genes such as psbA (photosynthesis), rbcL (carbon-fixation), and nifH (nitrogen- fixation). In addition, the expression response of genes which encode for antioxidant enzymes such as katE and cat (catalase) and superoxide dismutase (sodA), were also measured. For the antioxidant enzyme activity analysis, cells with scytonemin produced less antioxidant activity than those without scytonemin, regardless of the presence or absence of oxidative stress. In the evaluation of the gene expression response, the results were more variable. Gene expression of nifH was upregulated in cells with scytonemin and oxidative stress, while the expression of rbcL was downregulated under similar conditions. In cells with scytonemin, expression of cat and katE were upregulated, while sodA was downregulated. Interestingly scytonemin appeared to suppress the antioxidant enzyme activity response while increasing the transcriptional response of catalase enzymes. This discrepancy could be explained by the fact that gene expression occurs before the translational or enzymatic response. Since the cells were only stressed for 30 min it is possible that the corresponding functional proteins were not active at the time of cell harvesting. Future studies will involve a temporal analysis of this response in order to better understand the contributions of scytonemin in coping with oxidative stress in N. punctiforme.http://opus.ipfw.edu/stu_symp2017/1002/thumbnail.jp