Photosynthetic Growth and Energy Conversion in an Engineered Phototroph Containing Thermochromatium tepidum Light-Harvesting Complex 1 and the Rhodobacter sphaeroides Reaction Center Complex

Abstract

Light-harvesting complex 1 (LH1) of the thermophilic purple sulfur bacterium Thermochromatium tepidum can be expressed in the purple non-sulfur bacterium Rhodobacter sphaeroides and forms a functional RC-LH1 complex with the native Rba. sphaeroides reaction center (Nagashima, K. V. P., et al. Proc. Natl. Acad. Sci. U. S. A. 2017, 114, 10906−10911). Although there is a large uphill energy gap between Tch. tepidum LH1 and the Rba. sphaeroides RC in this chimeric complex, it has been shown that light energy can be transferred, consistent with that seen in the native Rba. sphaeroides RC-LH1 complex. In this study, the contribution of this chimeric complex to growth and photosynthetic energy conversion in the hybrid organism was quantified. The mutant synthesizing this chimeric complex was grown phototrophically under 940 nm light-emitting diode (LED) light preferentially absorbed by Tch. tepidum LH1 and showed faster growth at low intensities of this wavelength than both a mutant strain of Rba. sphaeroides lacking LH2 and a mutant lacking all light-harvesting complexes. When grown with 850 nm LED light, the strain containing the native Rba. sphaeroides LH1-RC grew faster than the chimeric strain. Electron transfer from the RC to the membraneintegrated cytochrome bc 1 complex was also estimated by flash-induced absorption changes in heme b. The rate of ubiquinone transport through the LH1 ring structure in the chimeric strain was virtually the same as that in native Rba. sphaeroides. We conclude that Tch. tepidum LH1 can perform the physiological functions of native LH1 in Rba. sphaeroides.

Calcium and the ecology of photosynthesis in purple sulfur bacteria

“…sphaeroides ); the LH1 of the hybrid complex contained Ca 2+ , and its Q y band at 915 nm was precisely that of wild‐type Tch. tepidum (Nagashima et al, 2017, 2021). Moreover, the major carotenoid in Rba.…”

Creating value from purple phototrophic bacteria via single-cell protein production

“…PPB perform anoxygenic photosynthesis, which does not produce oxygen because water does not serve as electron donor [1]. Instead, PPB use a diversity of organic donors, such as acetate and succinate, that serve as both carbon and electron source, and inorganic donors such as H2, H2S, or Fe 2+ , for anaerobic photoheterotrophic and spectrum, >850 and >1000 nm [3], while carotenoids have accessory light harvesting functions and also serve for photo-inhibition protection in the visible range (400-600 nm) [4]. The utilisation of light as energy source enables biomass yields close to unity on chemical oxygen demand (COD) basis during photoheterotrophic growth, and the exclusive capability of absorbing NIR wavelengths allows effective selection of PPB in non-sterile environments, such as wastewater [5].…”