Ethanoligenens, a novel ethanologenic and hydrogen-producing genus, has capability of hydrogen production at low pH. A [FeFe]-hydrogenase gene with [4Fe-4S] and [2Fe-2S] clusters from Ethanoligenens harbinense YUAN-3 was cloned and overexpressed in a non-hydrogen-producing Escherichia coli BL-21. This hydA gene consisted of an open reading frame of 1743 bp encoding 580 amino acids with an estimated molecular weight of 63 188.1 Da. Six characteristic sequence signatures were present within the H-cluster domain of [FeFe]-H(2)ases, and three of them were described previously. The overexpressed and purified hydrogenases from recombinant cells showed catalytic activity in vitro and in vivo. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.