the unique economic pressures of wartime sometimes provide incentive for scientific discovery. Two examples from the First WorldWar involve the production of organic solvents by the microbial fermentation of readily available carbohydrates,such as starch or molasses. The German side needed glycerol to make nitroglycerin. At onetime the Germans had imported their glycerol,but such imports were prevented by the British naval blockade. The German scientist Carl Neu-berg knew that trace levels of glycerol were usually produced during the alcoholic fermentation of sugar by Saccharomyces cerevisiae.He sought to develop a modified fermentation in which the yeasts would produce glycerol instead of ethanol. Normally acetaldehyde is reduced to ethanol by NADH and alcohol dehydrogenase (figure 9.10,pathway 2). Neuberg found that this reaction could be prevented by the addition of 3.5%sodium sulfite at pH 7.0. The bisulfite ions reacted with acetaldehyde and made it unavailable for reduction to ethanol. Because the yeast cells still had to regenerate their NAD even though acetaldehyde was no longer available ,Neuberg suspected that they would simply increase the rate of glycerol synthesis. Glycerol is normally produced by the reduction of dihydroxyacetone phosphate (a glycolytic intermediate) to glycerol phosphate with NADH, followed by the hydrolysis of glycerol phosphate to glycerol. Neuberg’s hunch was correct,and German breweries were converted to glycerol manufacture by his procedure,eventually producing 1,000 tons of glycerol per month. Glycerol production by S. cerevisiae was not economically competitive under peacetime conditions and was ended. Today glycerol is produced microbially by the halophilic alga Dunaliella salina,in which high concentrations of intracellular glycerol accumulate to counterbalance the osmotic pressure from the high level