Impact of spectrally separated light on Rhodobacter sphaeroides

There is a fine balance between the amount and type of light needed for efficient photosynthesis before oxidative stress and photodamage occurs. In addition, many organisms are able to prevent excess light energy from reaching their photosynthetic active sites as a protection strategy. However, this homeostasis is not clearly understood and there are many remaining questions in how wildly fluctuating energy from the environment is efficiently moderated to a usable form without complete disruption of photosynthetic systems, especially under ever changing conditions due to climate change. Although much research has focused on the stress response of plants to excess light, there is a lack of research quantifying how organisms are affected by and adapt to different wavelengths, intensities, and overall incident spectra of light. Photosynthetic microbes are a prime target for such studies because of their relatively simple photosynthetic apparatus compared to plants, ease of manipulation in mutagenesis experiments, and the overall simplicity of experimental design when working with a single celled organism.

By utilizing a spectrally separated supercontinuum laser light source aimed at a “Bacteria Farm” system, developed by Mehmet Kilinc, a physics graduate student in Dr. Nathan Gabor’s research group, we grow bacterial cultures under predefined wavelengths and power. From these growths, we quantify the response of R. sphaeroides to wavelength and intensity of light through differences in the transcriptome of R. sphaeroides resulting from energy exposure. RNA-sequencing is conducted using Illumina’s HiSeq platform after rRNA depletion in order to perform a deeper analysis of the metatranscriptome under each light condition without interference from ribosomal RNA. This project begins to help identify essential genes in light stress response aimed at testing the idea that photosynthetic systems have evolved to suppress power fluctuations rather than maximize energy absorption. Analyzing the transcriptomic profile of R. sphaeroides under different energetic fluctuations will characterize the mechanism through which this bacterium adapts and responds to spectrally and intensity-separated light in order to utilize available light energy efficiently.