Growth and fermentation of bacteria near their minimum temperature

The object of this paper was to study the minimum tempera-ture of fermentation separately from that for growth, and to explain, if possible, the cause for a minimum temperature. Since both these life functions are chemical reactions, they should continue, though at a greatly reduced speed, until the medium freezes solid. This is certainly not always the case with the growth of bacteria; most of them completely cease to grow at temperatures 5 to 10 or more degrees above the freezing point. EXPERIMENTAL APPROACH A first set of experiments was carried out with the technique used by Rahn (1932 p. 134) using Streptococcus lactis, S. fecalis, S. glycerinaceus, S. cremoris, S. liquefaciens, S. mastitidis and LactobaciUus acidophilus. The bacteria were cultivated at 30'C. in a heavily buffered lactose broth (for the Lactobacillus, tomato juice was added). After twenty-four to thirty-six hours, the cultures were neutralized and centrifuged. The bacterial sedi-ment, after being cooled to the desired temperature, was sus-pended in sterile milk of the same temperature., This series demonstrated the influence of low temperature upon fermentation, independent of growth. Some of the results are given in figure 1. I It was intended to make the inoculum so large that no multiplication would take place, but with Lactobacillus and S. glycerinaceus, this aim was not accom-plished as the frequent plate counts revealed. The inoculum was, in million cells per cubic centimeter, with Lactobacillus 6, with S. glycerinaceus 18, with S. lactis 250, with S. fecalis 400 and with S. liquefaciens 500. The sigmoid curves of S. glycerinaceus show plainly that the number of cells slowly increased