Chementator: Feed sugar to these bacteria and they’ll produce hydrogen
By Edited by Gerald Ondrey |
Azotobacter are nitrogen-fixing bacteria that do a useful job in soil by converting N 2 to ammonia. As a side reaction they also produce hydrogen, most of which they oxidize for their own energy consumption. In a project of the U.S. Dept. of Agriculture’s Soybean and Nitrogen Fixation Unit (USDA; www.ars.usda.gov) and North Carolina State University (Raleigh, N.C.), scientists have induced these bacteria to produce more H 2 and to release it rather than use it.
The bacteria use any one of three enzymes to produce NH3 and H2: a molybdenum nitrogenase, a vanadium nitrogenase and an iron nitrogenase. The Mo nitrogenase is the most efficient for N2 conversion, using 75% of its electrons to make ammonia and only 25% to reduce protons to H2, explains Paul Bishop, a USDA microbiologist (recently retired). The iron nitrogenase, in contrast, uses 50% of its electrons to make H2.
Working with species that have the Mo and iron enzymes, the researchers use tungsten to inactivate both the molybdenum enzyme and a gene that is required for the uptake of hydrogen, so that only the iron enzyme functions and all of the H2 is released. This is achieved by cultivating the bacteria in an aqueous solution of mixed salts, including sodium tungstate.…