Biohydrogen production of obligate anaerobic archaeon NA1 under oxic conditions via overexpression of -encoding hydrogenase genes.

Background: The production of biohydrogen (H) as a promising future fuel in anaerobic hyperthermophiles has attracted great attention because H formation is more thermodynamically feasible at elevated temperatures and fewer undesired side products are produced. However, these microbes require anoxic culture conditions for growth and H production, thereby necessitating costly and time-consuming physical or chemical methods to remove molecular oxygen (O). Therefore, the development of an O-tolerant strain would be useful for industrial applications.

Results: In this study, we found that the overexpression of -encoding hydrogenase genes in NA1, an obligate anaerobic archaeon and robust H producer, enhanced O tolerance. When the recombinant FO strain was exposed to levels of O up to 20% in the headspace of a sealed bottle, it showed significant growth. Whole transcriptome analysis of the FO strain revealed that several genes involved in the stress response such as chaperonin β subunit, universal stress protein, peroxiredoxin, and alkyl hydroperoxide reductase subunit C, were significantly up-regulated. The O tolerance of the FO strain enabled it to grow on formate and produce H under oxic conditions, where prior O-removing steps were omitted, such as the addition of reducing agent NaS, autoclaving, and inert gas purging.

Conclusions: Via the overexpression of genes, the obligate anaerobic archaeon NA1 gained the ability to overcome the inhibitory effect of O. This O-tolerant property of the strain may provide another advantage to this hyperthermophilic archaeon as a platform for biofuel H production.