Examining the effects of alternative electron transport in cyanobacteria

The photosynthetic apparatus utilizes light-dependent electron flow to generate a tightly coupled ratio of ATP/NADPH during linear electron flow. Under environments that would negatively affect photosynthetic productivity, changes in the demand and production of ATP and NADPH for metabolic pathways may arise, and the photosynthetic machinery must balance the generation and consumption of both ATP and NADPH through alternative electron transport (AET) processes.  In an effort to determine the effects of modulating the ATP/NADPH levels through these mechanisms, we have characterized genetically-engineered strains of the cyanobacteria Synechococcus sp. strain PCC 7002 (PCC 7002) overexpressing heterologous flavodiiron proteins to stimulate the Mehler pathway, or NADPH dehydrogenase subunits enhancing cyclic electron flow. We have demonstrated that enhancement of AET through these processes improves growth rates, increases tolerance to abiotic stresses, as well as alters carbohydrate metabolism. We believe our study would be invaluable to a deeper understanding of the regulation that govern the much of metabolism, while also validating, and leading to more predictive genome-scale metabolic models for cyanobacteria.