Gene expression of a two-component regulatory system associated with sunscreen biosynthesis in the cyanobacterium Nostoc punctiforme ATCC 29133

As phototrophic bacteria, cyanobacteria are continually exposed to ultraviolet radiation (UVR) as they harvest solar energy. Long-wavelength ultraviolet radiation (UVA) in particular contributes to most of the UVR that reaches the Earth’s surface and damages living cells through photooxidative stress. In phototrophs, this can lead to harmful photosensitized light-harvesting proteins and pigments. To mitigate damage to the cell, some cyanobacteria produce a UVAabsorbing pigment in the extracellular sheath, known as scytonemin. Scytonemin is a heterocyclic, dimeric molecule that is produced by some cyanobacteria upon induction by UVA. It is hypothesized that it is regulated by a putative two-component regulatory system (TCRS; NpF1277 and NpF1278) that is upstream and adjacent to the scytonemin biosynthetic gene cluster in the cyanobacterium Nostoc punctiforme ATCC 29133. TCRSs are commonly made up of a sensor kinase which senses the environmental stress and a response regulator that is activated by the sensor kinase to initiate gene expression of a cellular response. The expression of the TCRS genes NpF1277 and NpF1278 in N. punctiforme have been evaluated in response to several environmental stressors: UVA, short-wavelength UVB, oxidative stress, and high light. Cells were stressed for 20, 40, and 60 minutes and the expression levels of the TCRS genes were compared to unstressed controls using quantitative PCR. Cells under UVA, UVB, and high light stress showed an up-regulation of both TCRS genes by 20 minutes. Aside from an up-regulation for both genes after 40 minutes of UVB and 60 minutes of high light, 40 and 60 minutes of stress generally resulted in either a down-regulation or no significant change for all four stressors. This research shows how regulation occurs for the sunscreen scytonemin in cyanobacteria and how they cope with stress under certain environmental conditions.http://opus.ipfw.edu/stu_symp2015/1035/thumbnail.jp