Tfx family transcriptional regulator regulates H2 metabolism in the hyperthermophilic archaeon Thermococcus onnurineus NA1

Abstract

The Tfx family DNA-binding protein has been identified in Methanobacterium thermoautotrophicum to activate transcription of a gene cluster (fmdECB) encoding molybdenum formylmethanofuran dehydrogenase. The TON_1525 protein, a homolog of the Tfx protein, was first demonstrated in the hyperthermophilic archaeon Thermococcus onnurineus NA1 as a transcriptional repressor of a gene cluster encoding carbon monoxide dehydrogenase, hydrogenase and Na+/H+ antiporter. The T55I mutant protein had weak binding affinity to the promoter, so the transcription level of genes was increased. To elaborate our results, we extended our study to gene regulation by the TON_1525 at the genome level. We constructed a gene deletion mutant (Δ1525) and investigated transcriptome changes. Transcriptome profiling revealed that the expression levels of 263 transcripts were significantly increased (≥1.5-fold), while the expression levels of 88 transcripts were decreased (≤0.5-fold). Expression levels of hydrogenase genes involved in the consumption or production of H2 were significantly altered. The mbh (membrane-bound hydrogenase) and mch (membrane-bound carbon monoxide-dependent hydrogenase) genes were up-regulated, whereas the mfh2 (membrane-bound formate-dependent hydrogenase), sulfI (soluble hydrogenase I) and frhAGB (frhAGB-encoded hydrogenase) genes were down-regulated. Based on the transcriptome data, we investigated the H2 production of the 1525 mutant under maltodextrin or CO-supplemented conditions. The maximum H2 production rate of the 1525 mutant was greatly enhanced for both substrates compared to the wild-type strain. These results indicate that the TON_1525 protein has the potential to affect the expression of various genes and consequently regulate the metabolism of T. onnurineus NA1. This study provides a perspective for understanding the function of the Tfx family DNA-binding proteins.