H-dependent formate production by hyperthermophilic Thermococcales: an alternative to sulfur reduction for reducing-equivalents disposal.

Removal of reducing equivalents is an essential catabolic process for all microorganisms to maintain their internal redox balance. The electron disposal by chemoorganotrophic Thermococcales generates H by proton reduction or HS in presence of S. Although in the absence of S growth of these (hyper)thermopiles was previously described to be H-limited, it remains unclear how Thermococcales could be present in H-rich S-depleted habitats.