Characterization and hydrogen production performance of a novel strain Enterococcus faecium INET2 isolated from gamma irradiated sludge

A novel hydrogen-producing strain was isolated from the gamma irradiated sludge and identified as Enterococcus faecium INET2 by 16S rRNA gene analysis. The hydrogen production performance by E. faecium INET2 was investigated at temperature of 25-40 °C, initial pH of 5-10, substrate concentration of 5-20 g/L glucose and inoculation ratio of 5-30%. The suitable condition for hydrogen production was determined to be 35 °C, initial pH 7, 15 g/L glucose and 10% inoculation ratio. E. faecium INET2 was immobilized using polyvinyl alcohol (PVA)-sodium alginate and applied for hydrogen production. The maximum cumulative hydrogen production and hydrogen yield were 130 mL H2/100 mL, 1.16 mol H2/mol glucose for free cells, and 202 mL/100 mL, 1.69 mol H2/mol glucose for the immobilized cells. Acetic acid and butyric acid were the major volatile fatty acids formed during the fermentation process, and the process was dominated by acetate-type fermentation. These results indicate that E. faecium INET2 is a promising candidate for fermentative hydrogen production.