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DIFFERENTIAL MEDIUM FOR SELECTION AND ENUMERATION OF MEMBERS OF THE GENUS PSEUDOMONAS1

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PMC
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  • Biology

Abstract

TABLE 2. Isotope balances after addition of ethanol-i_-C4 to ruminal contents Radioactivity of fractions (count/min) Expt Bovine ration Incubation Volatile Residual CO Liquid Solid ethanol acids ethanol residue residue hr 1 Alfalfa hay 3 103,500 30,000 76,000 186 626 1,200 2 Alfalfa hay 1.5 76,300 11,900 62,200 158 1,458 444 3 Alfalfa hay (3) 1.5 103,500 36,100 62,900 159 1,560 516 and grain (23) 4 Alfalfa hay, 1.5 58,300 16,100 43,100 grass pasture comes endergonic as H2 concentration increases, diminishing the over-all free energy of the fer- mentation. In mixed culture such as in the rumen, the hydrogen concentration is kept low (0.05% in the rumen) by participating in exergonic reactions forming methane, propionic acid, and butyric acid. Ethanol is ordinarily formed in bacteria by re- duction of acetyl-coenzyme A (CoA). The acetyl- CoA concentration is usually low, and with low H2 concentration the ethanol concentration would also be small. The enzyme needed in the con- version to ethanol may not form unless some intermediate, which serves as an inducer, reaches the threshold concentration for induction. Approximately 0.05 to 0.1 ,umole of tracer was used in each experiment of Table 2. The 400 ,umoles of ethanol in the manometric experiments were converted at a rate of 1 Amole/min, a much greater rate than that in the tracer experiments. Similar evidence that ethanol concentration affected the absolute rate of conversion was ob- tained by adding 16 ,imoles of unlabeled ethanol to one of two vessels, both receiving 0.05 MAmoles of the labeled material. Of the 16.05,moles, 10% (1.7 ,umoles) was converted to acetic acid; in the control, 26% (0.013 umoles) was converted in an equal period. In the manometric experiments with 400 ,umoles of ethanol, 25% (ca. 100 ,umoles) was converted. These values suggest a conversion of ethanol in a reaction(s) in which concentration is an important factor influencing the rate. The re- actions appear to come to equilibrium when 10 to 25% of the ethan

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