Thermococcus onnurineus NA1, an obligate anaerobic hyperthermophilic
archaeon, showed variable oxygen (O2) sensitivity
depending on the types of substrate employed as an
energy source. Unexpectedly, the culture with yeast extract
as a sole energy source showed enhanced growth by 2-fold
in the presence of O2. Genome-wide transcriptome analysis
revealed the upregulation of several antioxidant-related genes
encoding thioredoxin peroxidase (TON_0862), rubrerythrin
(TON_0864), rubrerythrin-related protein (TON_0873),
NAD(P)H rubredoxin oxidoreductase (TON_0865), or thioredoxin
reductase (TON_1603), which can couple the detoxification
of reactive oxygen species with the regeneration
of NAD(P)+ from NAD(P)H. We present a plausible mechanism
by which O2 serves to maintain the intracellular redox
balance. This study demonstrates an unusual strategy of an
obligate anaerobe underlying O2-mediated growth enhancement
despite not having heme-based or cytochrome-type
proteins.