Maximizing reductant flow into microbial H2 production

► Cellular reductant flow influences microbial H2 production. ► Heterologous hydrogenase expression could increase H2 yield in facultative anaerobes. ► Eliminating pathways that compete for electrons can increase H2 production. ► Biomass accumulation is a major electron sink in photosynthetic bacteria. ► Use of protein fusions could increase electron flow into H2 production.