Hydrogen Production by the Thermophilic Bacterium, Thermotoga neapolitana

Virtually all members of the order Thermotogales have demonstrated the ability to produce hydrogen and some members of this order produce considerably greater quantities than the rest. With one representative of this order, Thermotoga neapolitana, we have consistently obtained accumulations of 25-30% hydrogen with carbon dioxide as the only other prominent byproduct of the batch reaction (12-15%). In contradistinction to information widely disseminated in the literature, we have also found that most members of this order tolerate and appear to utilize moderate amounts of oxygen in the gaseous phase of the batch reactor (6-12%), with no apparent decrease in hydrogen production. Hydrogen accumulation has been widely reported to inhibit growth of members of the Thermotogales. While this may be true at very high hydrogen tensions, we have noted hydrogen generation during both the log and stationary phase. To maximize hydrogen production and minimize production of hydrogen sulfide, inorganic sulfur donors are avoided and the cysteine concentration in the medium is increased. Different members of the order Thermotogales have been demonstrated by the authors and by others to utilize a wide variety of feedstocks, including complex carbohydrates and proteins. Our results suggest that organisms within this order have the potential to utilize a variety of organic wastes and to cost-effectively generate significant quantities of hydrogen gas.