Current status of the metabolic engineering of microorganisms for biohydrogen production

The improvement of H₂ production capabilities of hydrogen (H₂)-producing microorganisms is a challenging issue. Microorganisms have evolved for fast growth and substrate utilization rather than H₂ production. To develop good H₂-producing biocatalysts, many studies have focused on the redirection and/or reconstruction of cellular metabolisms. These studies included the elimination of enzymes and carbon pathways interfering or competing with H₂ production, the incorporation of non-native metabolic pathways leading to H₂ production, the utilization of various carbon substrates, the rectification of H₂-producting enzymes (nitrogenase and hydrogenase) and photophosphorylation systems, and in silico pathway flux analysis, among others. Owing to these studies, significant improvements in the yield and rate of H₂ production, and in the stability of H₂ production activity, were reached. This review presents and discusses the recent developments in biohydrogen production, with a focus on metabolic pathway engineering.