Abstract
Purple non-sulfur bacteria (PNSB) are metabolically versatile microorganisms which inhabit the most diverse environments by taking advantage of remarkably efficient photosynthetic machinery. Studies carried during the last decades have suggested that this high efficiency is mainly a result of quantum coherent interactions occurring between the electronic states of photosynthetic pigments and their surrounding intramolecular, protein and solvent motions. Although such hypothesis is theoretically well established and has been supported by the presence of “quantum beats” detected during 2D spectroscopy analyses, experimental data obtained in vivo and the evolutionary implications of such mechanism are still missing. In the present work, I describe my attempts to create a system for the performance of such experimental studies using the light-harvesting complex 2 (LH2) expressed by PNSB as model. The approach chosen for this purpose was based on the modification of the LH2 protein scaffold to tune the absorption properties and, consequently, the electronic states of the pigments. During the efforts to create a platform for the expression of LH2 spectral variants, the genome and transcriptome of Rhodoblastus acidophilus subject to different treatments have been analysed. The data revealed an extremely versatile microorganism with a complex network for regulation of photosynthesis. The second part of the project consisted of the expression and spectral analysis of LH2 variants being expressed in the model PNSB Rhodobacter sphaeroides. The results obtained in this study suggest that the LH2s variants expressed by PNSB reflects the intricate tunning of their quantum properties towards the optimum light-harvesting efficiencies which is dependent on the environmental conditions. Ultimately, this work constitutes a foundation for the development of bioinspired sunlight harvesting technologies and has implications for our understanding of the evolution of bacterial photosynthesis and quantum mechanical effects in biology.