Disrupting Calvin cycle phosphoribulokinase activity in Rhodopseudomonas palustris increases the H2 yield and specific production rate proportionately

Abstract

Anoxygenic phototrophs, like Rhodopseudomonas palustris, can convert light energy and electrons from organic waste into H2 gas, a potential biofuel. During phototrophic growth on organic compounds, the CO2-fixing Calvin cycle competes against H2 production for electrons. Here we address why genetically disrupting the CO2-fixing enzyme, ribulose 1,5-bisphosphate carboxylase (Rubisco), increases the H2 yield but not the specific H2 production rate. We hypothesized that remaining upstream phosphoribulokinase (PRK) activity negatively impacts growth and thereby the specific H2 production rate, likely due to the accumulation of ribulose-1,5-bisphosphate, the substrate for Rubisco. In agreement with our hypothesis, deletion of PRK resulted in proportional increases to both the H2 yield and the specific production rate. Thus, even though Rubsico is traditionally a more common target to eliminate Calvin cycle activity we propose PRK as a favorable alternative to avoid undesirable pleiotropic effects.