Even so, are not the denitrifying bacteria dangerous parasites that turn useful nitrate into useless molecular ? This was thought to be true at the turn of the century when denitrifying bacteria first were discovered. A prominent British biochemist painted a bleak picture of world starvation unless an industrial process for fixing atmospheric nitrogen was found quickly. Fortunately, the race for survival between us and Pseudomonas denitrificans was a phony race. The denitrifying bacteria assist other life forms by preventing all of the world's nitrogen supply from slowly becoming locked up in mineral deposits such as nitrates. They keep the nitrogen circulating. The nitrogen gas that they produce eventually is fixed again by other bacteria, lightning discharges, and industrial chemistry, and ultimately feeds back into the biological cycle.

P. denitrificans is not a villain, but we may be when we upset the natural nitrogen cycle with huge supplies of industrially fixed ammonia and nitrates. When nutrients become too plentiful, algae and other life forms "explode" in population to the point where they deplete the available oxygen supply and all die. This process is known as eutrophication ("good" + "feeding"), and its ill effects have been seen already in Lake Erie, polluted both by industry and by runoff from agricultural fertilizers. The end result is a lake choked with algae, devoid of oxygen, and filled with dead fish. In the balance of nature, too much can be as disastrous as too little.