Reported hydrogen yields were quite low, but conditions were not optimized.
More commonly, hydrogen fermenting bacteria are thought to contain a [FeFe] hydrogenase.
However, their occurrence in the environment, at least in an initial metagenomic survey, appears to be quite limited [53], and this is borne out by a recent blast search of over one billion base pairs of non-redundant sequence where only 10 hits to a [FeFe] hydrogenase bait sequence were found [54].