Fig. 1.
A Venn diagram displaying comparison between distinguished H2 producers with respect to desirable properties an ideal H2 producer may possess. A, thermophilic; B, has specific vectors/tools designed for genetic modification(s); C, possesses Fd-dependent hydrogenases; D, is not auxotrophic to any amino acids; E, has ability to degrade a wide range of biomass; F, can metabolize multiple sugars simultaneously (absence of carbon catabolite repression); G, when under stress shifts metabolism to useful by-products; H, is tolerant to high osmotic stress exerted by high substrate/by-product concentrations and I, is oxygen-tolerant. (Asterisk, note: property F is also present in Thermococcales and is indeed absent from other genera as depicted)