Bacterial Utilization of Low Concentrations of Organic Matter

Abstract

Although several investigators have studied the effect of organic nutrients upon the growth of microorganisms, most of the experiments have been concerned with concentrations which are much higher than those which occur in soil solutions, sea water and other natural environments. Ac- cording to Rahn (1932) the concentration of food does not influence the rate of growth of bacteria except when the concentration is very low, 0.01 to 0.1 per cent. Penfold and Norris (1912), Hucker and Carpenter (1927), Friedlein (1928), Bigger (1937) and others report that the minimum concentration of organic nutrients required for the multiplication of heterotrophs ranges from 0.001 to 0.01 per cent or 10 to 100 mgm./l. That many bacteria multiply and are otherwise physiologically active in very Although several investigators have studied the effect of concentration of mineral media when the concentration of organic nutrients is less than 0.1 mgm./l. There were indications that lower concentrations might provide for bacterial activity. The following experiments were designed to determine the effect of the concentration of various kinds of organic matter upon its rate of utilization by bacteria. dilute nutrient solutions is manifest from the abundance of bacteria in lake water (Henrici, 1939) and sea water (Benecke, 1933). The organic content of sea water is generally less than 5 mgm./l., yet during the storage of sea water in the laboratory the bacteriail population usually increases from a few hundred to several million bacteria per ml. (Waksman and Carey, 1935a). Bacterial multiplication is accompanied by the evolution of carbon dioxide, oxygen con- sumption, ammonia production, nitrate reduction and other biochemical changes (ZoBell and Anderson, 1936). Similar changes have been noted in lake water (ZoBell, 1940) which contained less than 10 mgm. of organic matter per liter. Butterfield (1929) found that after an extended lag period Aerobacter aerogenes multiplied slowly in a solution containing only 0.5 mgm./l. each of glucose and peptone. Heukelekian and Heller (1940) found that when glass beads were present to augment the area of solid surface, Escherichia coli grew in either glucose or peptone solutions as dilute as 0.5 mgm./l. Recently ZoBell and Grant (1942) reported that marine bacteria multiply in Now at Brooklyn College, Brooklyn, N. Y. Assisted by Grant No. 555 from the American Philosophial Society. IContribution from the Scripps Institution of Oceanography, New Series No. 199. 2 555