Liberating photoinhibition through extracellular extraction of photosynthetic electrons in anoxygenic phototrophic bacteria

Anoxygenic photosynthetic bacteria (APB) are crucial to global nutrient cycles and pollutant transformation but often face metabolic limitations due to photoinhibition. This study shows that the extracellular extraction of surplus photosynthetic electrons alleviates photoinhibition in Rhodopseudomonas palustris, enabling it to exceed its intrinsic photosynthetic capacity and efficiently convert high-intensity light into biomass. In three batch experiments, the use of an electrode at 0.4 V to guide the excess electrons to outside the cell increased nitrogen and carbon photoassimilation rates by 3.59 and 2.34 times, respectively, along with a 35.0 % boost in biomass in R. palustris, compared to the control group without the electrode under photoinhibitory light conditions (80,000 lx; 30 +/- 1 degrees C). Nitrogen, carbon, and biomass were 33.6 %, 6.6 %, and 17.0 % higher than the values for R. palustris normally cultivated under optimal light intensity. Coenzyme Q facilitates the extraction of photosynthetic electrons, restoring intracellular redox balance and enabling adaptation to high light intensity by increasing NADH/NAD+ and NADPH/NADP+ ratios. Moreover, this process upregulates genes associated with organelle function, transmembrane electron transport, and ATP synthesis. These findings provide new insights into the role of extracellular electron transfer in bacterial metabolism and suggest a promising strategy to enhance the productivity of APB under challenging environmental conditions.