CO-dependent bio-hydrogen production by the hyperthermophilic archaeon, Thermococcus onnurineus using sea-water medium

Abstract

The hyperthermophilic archaeon, Thermococcus onnurineus which was isolated from deep-sea hydrothermal vent area has been reported to be able to grow on carbon monoxide (CO) evolving hydrogen (H2) in a growth-associated manner. In this study, we developed sea-water medium (SW) and optimized its composition by using response surface methodology (RSM) to maximize the CO-dependent H2 production by T. onnurineus. The SW medium was developed simply by supplementing the essential components in cell growth among the compositions of the MYC medium, which was control medium, to sea-water. From a series of batch experiments in serum bottles, it was observed that T. onnurineus was able to grow well showing the similar optical density to MYC medium in the sea-water supplemented with the same concentrations of yeast extract, CO, FeSO4, EDTA, trace elements and vitamins as those in MYC medium. Then, using SW medium, the RSM-based optimization was conducted to maximize H2 production by T. onnurineus. Based on the five-level central composite design (CCD) with 3 variables of CO supply rate as an energy source, initial yeast extract concentration as a carbon and nitrogen source and agitation speed of bio-reactor as a key factor for gas-liquid mass transfer, 17 batch experiments were carried out in a 2.5L bio-reactor with working volume of 1L. As a result, the statistically significant model predicted the maximum H2 production rate (HP, we developed sea-water medium (SW) and optimized its composition by using response surface methodology (RSM) to maximize the CO-dependent H2 production by T. onnurineus. The SW medium was developed simply by supplementing the essential components in cell growth among the compositions of the MYC medium, which was control medium, to sea-water. From a series of batch experiments in serum bottles, it was observed that T. onnurineus was able to grow well showing the similar optical density to MYC medium in the sea-water supplemented with the same concentrations of yeast extract, CO, FeSO4, EDTA, trace elements and vitamins as those in MYC medium. Then, using SW medium, the RSM-based optimization was conducted to maximize H2 production by T. onnurineus. Based on the five-level central composite design (CCD) with 3 variables of CO supply rate as an energy source, initial yeast extract concentration as a carbon and nitrogen source and agitation speed of bio-reactor as a key factor for gas-liquid mass transfer, 17 batch experiments were carried out in a 2.5L bio-reactor with working volume of 1L. As a result, the statistically significant model predicted the maximum H2 production rate (HP