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

Abstract

BackgroundThe production of biohydrogen (H-2) as a promising future fuel in anaerobic hyperthermophiles has attracted great attention because H-2 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-2 production, thereby necessitating costly and time-consuming physical or chemical methods to remove molecular oxygen (O-2). Therefore, the development of an O-2-tolerant strain would be useful for industrial applications.ResultsIn this study, we found that the overexpression of frhAGB-encoding hydrogenase genes in Thermococcus onnurineus NA1, an obligate anaerobic archaeon and robust H-2 producer, enhanced O-2 tolerance. When the recombinant FO strain was exposed to levels of O-2 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 subunit, universal stress protein, peroxiredoxin, and alkyl hydroperoxide reductase subunit C, were significantly up-regulated. The O-2 tolerance of the FO strain enabled it to grow on formate and produce H-2 under oxic conditions, where prior O-2-removing steps were omitted, such as the addition of reducing agent Na2S, autoclaving, and inert gas purging.ConclusionsVia the overexpression of frhAGB genes, the obligate anaerobic archaeon T. onnurineus NA1 gained the ability to overcome the inhibitory effect of O-2. This O-2-tolerant property of the strain may provide another advantage to this hyperthermophilic archaeon as a platform for biofuel H-2 production.