초록
<P><B>Graphical abstract</B></P><P><ce:figure id='fig0005'></ce:figure></P><P><B>Highlights</B></P><P>► Cellular reductant flow influences microbial H<SUB>2</SUB> production. ► Heterologous hydrogenase expression could increase H<SUB>2</SUB> yield in facultative anaerobes. ► Eliminating pathways that compete for electrons can increase H<SUB>2</SUB> production. ► Biomass accumulation is a major electron sink in photosynthetic bacteria. ► Use of protein fusions could increase electron flow into H<SUB>2</SUB> production.</P> <P>Developing microbes into a sustainable source of hydrogen gas (H<SUB>2</SUB>) will require maximizing intracellular reductant flow toward the H<SUB>2</SUB>-producing enzymes. Recent attempts to increase H<SUB>2</SUB> production in dark fermentative bacteria include increasing oxidation of organic substrates through metabolic engineering and expression of exogenous hydrogenases. In photofermentative bacteria, H<SUB>2</SUB> production can be increased by minimizing reductant flow into competing pathways such as biomass formation and the Calvin cycle. One method of directing reductant toward H<SUB>2</SUB> production being investigated in oxygenic phototrophs, which could potentially be applied to other H<SUB>2</SUB>-producing organisms, is the tethering of electron donors and acceptors, such as hydrogenase and photosystem I, to create new intermolecular electron transfer pathways.</P>