Formate hydrogenlyase and formate secretion ameliorate H 2 inhibition in the hyperthermophilic archaeon Thermococcus paralvinellae

Summary Some hyperthermophilic heterotrophs in the genus Thermococcus produce H 2 in the absence of S° and have up to seven hydrogenases, but their combined physiological roles are unclear. Here, we show which hydrogenases in Thermococcus paralvinellae are affected by added H 2 during growth without S°. Growth rates and steady‐state cell concentrations decreased while formate production rates increased when T. paralvinallae was grown in a chemostat with 65 µM of added H 2(aq) . Differential gene expression analysis using RNA‐Seq showed consistent expression of six hydrogenase operons with and without added H 2 . In contrast, expression of the formate hydrogenlyase 1 ( fhl 1) operon increased with added H 2 . Flux balance analysis showed H 2 oxidation and formate production using FHL became an alternate route for electron disposal during H 2 inhibition with a concomitant increase in growth rate relative to cells without FHL. T. paralvinellae also grew on formate with an increase in H 2 production rate relative to growth on maltose or tryptone. Growth on formate increased fhl 1 expression but decreased expression of all other hydrogenases. Therefore, Thermococcus that possess fhl 1 have a competitive advantage over other Thermococcus species in hot subsurface environments where organic substrates are present, S° is absent and slow H 2 efflux causes growth inhibition.