Effects of Electrical Stimulation on Carbon Sequestration of Photosynthetic Bacteria: Response of the Photosynthetic Unit to Electrical Stimulation

Bioelectrochemical systems have been used to enhance the carbon sequestration of photosynthetic bacteria (PSB), but it is unclear whether the electrical stimulation affects the structure of membrane proteins involved in photochemical activity. In this study, the rate of CO2 fixation in the photosynthetic bacteria R. palustris increased with electrical stimulation, and the enhancement partly remained even after the power off. The CO2 fixation rate in electrical-stimulated PSB was 10% higher than in non-stimulated PSB, and the activity of the CO2 fixation enzyme Rubisco was 16% higher. This resulted from the improved light utilization efficiency of the photosynthetic units in R. palustris after electrical stimulation, particularly due to the enhancement of the primary reaction mediated by the light capture protein RC-LH1. The molar extinction coefficient of the light capture protein RC-LH1 increased from 3301 cm-1 mM-1 to 3733 cm-1 mM-1, and the maximum rate of the primary reaction increased from 6.88×10-3 e-RC-1s-1 to 8.66×10-3 e-RC-1s-1. Circular dichroism spectroscopy and Fourier transform infrared spectroscopy indicated that the electrical stimulation increased the dipole moment of the α-helix in RC-LH1 to facilitate the quinone transport in the primary reaction. Nuclear magnetic resonance spectroscopy revealed that the electrical stimulation increased the formation of hydrogen bonds in bacteriochlorophyll a for electron transition. This study investigated the response of photosynthetic bacteria to electrical stimulation, providing a distinct outlook on the electrochemical regulation of photosynthesis for carbon capture.