Hydrogen Production by Desulfurococcus fermentans
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Desulfurococcus fermentans is a hyperthermophilic archaeon growing optimally at 82°C. This microorganism is an obligate anaerobe with optimal growth pH of 6.0. It is capable of producing H2 as an end metabolic product using cellulose as growth substrate. The major goal of this study was to optimize the growth conditions for the production of H2 from various substrates such as cellulose, cellobiose, carboxymethyl cellulose (CMC), xylan, filter paper, avecil, starch and peptides. The highest cell density (2.83×108 cells/ml) was observed when yeast extract (0.2 g/L), starch (5 g/L) and xylan (4 g/L) were added to its growth media. The lowest generation time was shown to be 2.4 hours when yeast extract (0.2 g/L), starch (5 g/L) and cellobiose (4 g/L) were added to its growth medium. It was found that the growth of D. fermentans was obligately depended on the presence of yeast extract in the growth medium, and the H2 production was positively correlated to its growth. Cells of D. fermentans were cocci with diameters varying from 1 to 3 µm. The largest cell size was observed using scanning electron microscopy when it grew in medium containing yeast extract (10 g/L) and starch (5 g/L). Maximum hydrogen production of 12% (v/v) was achieved when yeast extract (0.2 g/L), starch (5 g/L) and carboxymethyl cellulose (4 g/L) were added to the growth medium. Further studies are required to obtain the specific yield of H2 from various substrates through the quantification of both the consumption of substrates and the production of H2 by D. fermentans.