초록
<P><B>Abstract</B></P> <P>Anoxygenic phototrophs, like <I>Rhodopseudomonas palustris,</I> can convert light energy and electrons from organic waste into H<SUB>2</SUB> gas, a potential biofuel. During phototrophic growth on organic compounds, the CO<SUB>2</SUB>-fixing Calvin cycle competes against H<SUB>2</SUB> production for electrons. Here we address why genetically disrupting the CO<SUB>2</SUB>-fixing enzyme, ribulose 1,5-bisphosphate carboxylase (Rubisco), increases the H<SUB>2</SUB> yield but not the specific H<SUB>2</SUB> production rate. We hypothesized that remaining upstream phosphoribulokinase (PRK) activity negatively impacts growth and thereby the specific H<SUB>2</SUB> 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 H<SUB>2</SUB> 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.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Elimination of Calvin cycle phosphoribulokinase increases both the H<SUB>2</SUB> yield and rate. </LI> <LI> H<SUB>2</SUB> production by nitrogenase can fully replace the Calvin cycle electron balancing role. </LI> <LI> Phosphoribulokinase is a preferred target versus Rubisco for enhancing H<SUB>2</SUB> production. </LI> </UL> </P>