Molecular Hydrogen (H2) Metabolism in Microbes: A Special Focus on Biohydrogen Production

In recent years, biohydrogen production (produced from renewable sources either biologically or photo-biologically) has attracted substantial interest from researchers worldwide because of its potential application as an alternative and clean fuel. Microbes not only produce molecular hydrogen (H2) but can also utilize it as an electron acceptor with the help of hydrogenases. The capability of microorganisms to use or produce H2 is deeply encrypted in their genes, which are transcribed as mRNA and finally translated to protein (some of which act as enzymes). Enzymes play a pivotal role during cellular metabolism that decides the fate of any metabolite. One needs to dig down at the genetic and proteomic levels to understand these complex cellular metabolisms and regulate the production of a metabolite (or product) of interest. In this chapter, we have discussed the microbial metabolism of molecular H2 with special emphasis on its production. Herein, we have first focused on genes for H2 metabolism and their origins across various species. Then, metabolic pathways involved in hydrogen metabolism have been discussed with an applied view—cofactors and coenzymes. Further, building blocks and targets for synthetic biology for the overproduction of H2 have been considered.