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24 The photosynthetic complexes of the thermophile Thermochromatium tepidum are of 25 considerable interest in biohybrid solar cell applications because of the capability of thermophilic 26 proteins to tolerate elevated temperatures. Synthetic operons encoding reaction centre (RC) and 27 light harvesting 1 (LH1) pigment-protein complexes of T. tepidum were expressed in the 28 mesophile Rhodobacter sphaeroides. The T. tepidum RC (TRC) was assembled, and functional 29 with the addition of menadione to populate the QA pocket. The production of the T. tepidum LH1 30 (TLH1) was increased by selection of a phototrophy-capable mutant after UV irradiation 31 mutagenesis, which yielded a hybrid RC-TLH1 core complex consisting of the R. sphaeroides 32 RC and T. tepidum TLH1, confirmed by the absorbance peak of TLH1 at 915 nm. Affinity 33 chromatography partial purification and subsequent sucrose gradient analysis of the hybrid RC34 TLH1 core complex indicated that this core complex assembled as a monomer. Furthermore, the 35 RC-TLH1 hybrid core complex was more tolerant of 70 °C temperature than the R. sphaeroides 36 RC-LH1 core complexes in both the dimeric and monomeric forms: after 1 h, the hybrid 37 complex retained 58% of the initial starting value, compared to 11 and 53% for the R. 38 sphaeroides RC-LH1 dimer and monomer forms, respectively. 39 40 Importance 41 This work is important because it is a new approach to bio-engineering of photosynthesis 42 proteins for potential use in bio-photovoltaic solar energy capture. The work establishes proof43 of-principle for future biohybrid solar cell applications. 44 45 on S etem er 1, 2017 by U iv of T exas at D allas ht://aem .sm .rg/ D ow nladed fom