Functional Expression of Gloeobacter Rhodopsin in PSI-Less Synechocystis sp. PCC6803.

Que Chen,Jos Arents,Srividya Ganapathy,Christiane Funk,Filipe Branco dos Santos,Otilia Cheregi,Willem J. de Grip,Klaas J. Hellingwerf,J. Merijn Schuurmans

doi:10.3389/fbioe.2019.00067

Abstract

The approach of providing an oxygenic photosynthetic organism with a cyclic electron transfer system, i.e., a far-red light-driven proton pump, is widely proposed to maximize photosynthetic efficiency via expanding the absorption spectrum of photosynthetically active radiation. As a first step in this approach, Gloeobacter rhodopsin was expressed in a PSI-deletion strain of Synechocystis sp. PCC6803. Functional expression of Gloeobacter rhodopsin, in contrast to Proteorhodopsin, did not stimulate the rate of photoheterotrophic growth of this Synechocystis strain, analyzed with growth rate measurements and competition experiments. Nevertheless, analysis of oxygen uptake and—production rates of the Gloeobacter rhodopsin-expressing strains, relative to the ΔPSI control strain, confirm that the proton-pumping Gloeobacter rhodopsin provides the cells with additional capacity to generate proton motive force. Significantly, expression of the Gloeobacter rhodopsin did modulate levels of pigment formation in the transgenic strain.

Highlights

Human society faces a growing tension between the increasing use of fossil, i.e., petroleum-based, fuel and the wish to decrease the alarming level of CO2 emission
A widely acclaimed proposal to achieve this is to expand the spectrum of photosynthetically active radiation (PAR) for phototrophic microorganisms
Solar energy conversion systems naturally exist that do function with light of wavelengths >700 nm, i.e., those oxygenic photosynthetic microorganisms that use chlorophyll d (Chl d) (Manning and Strain, 1943; Von Wettstein et al, 1995) or chlorophyll f (Chl f ) (Chen et al, 2010; Li et al, 2012; Ho et al, 2016), instead of chlorophyll a

Summary

INTRODUCTION

Human society faces a growing tension between the increasing use of fossil, i.e., petroleum-based, fuel and the wish to decrease the alarming level of CO2 emission. Solar energy conversion systems naturally exist that do function with light of wavelengths >700 nm, i.e., those oxygenic photosynthetic microorganisms that use chlorophyll d (Chl d) (Manning and Strain, 1943; Von Wettstein et al, 1995) or chlorophyll f (Chl f ) (Chen et al, 2010; Li et al, 2012; Ho et al, 2016), instead of chlorophyll a. These two alternative chlorophylls capture photons in the range of 700–720 and 700– 740 nm, respectively. Spectroscopic analysis shows that the Gloeobacter rhodopsin-expressing strain has a significantly altered absorption profile, suggesting that biosynthesis of photosynthetic pigments has been modulated in this strain

MATERIALS AND METHODS

Experiments With PCR

RESULTS AND DISCUSSION