| Abstrakt: |
Measurements of the apparent oxidation-reduction potentials established in a synthetic medium by the growth of Escherichia colishowed that many irregularities were encountered which were not present when determinations were made in peptone nutrient broth cultures of the same organism. It is the object of this paper to present a study of the factors involved in these irregularities. The elimination of such would make it possible to obtain consistent data from which valuable conclusions might be deduced.A vacuum tube null-point instrument drawing a maximum current of 10-11ampere was utilized in making the physical measurements. No polarization phenomena were observed and the apparatus gave calculated values for easily polarizable half cells. Bright platinum electrodes were used. A liquid medium made by weighing the requisite C.P. or analytical reagents and adding to redistilled water allowed the test organism, Escherichia coli, to grow vigorously. This basic solution, a slight modification of that of Koser and Saunders,1was composed of Na2HPO41.4 g, KH2PO41.0 g. NaCl 2.0 g. MgSO4(anhy.) 0.1 g, 1-asparagine 3.0 g, 1-tryptophane 0.2 g. d-glucose 2.0 g, and redistilled water 1 liter. Sterilization was accomplished by filtration. The final pH was 6.9. A nutrient broth medium used for comparison was composed of beef extract (Swift) 3.0 g, peptone (Difco) 10.0 g, NaCl 5.0 g, and redistilled water 500 ml. This was adjusted to a pH of 6.9, sterilized in the autoclave, and to it was added 500 ml of sterile phosphate buffer (pH 6.9 at 37.5 C). The buffer was present in a final concentration of M/30.Culture vessels consisted of 180 nil electrolytic beakers stoppered with rubber stoppers containing appropriate holes for the electrodes, for a stirring apparatus, for the agar-KCl bridge and to allow for gas exchange. The medium, previously inoculated with E. coli, Was pipetted into the electrode containing vessels after the latter had been sterilized in the autoclave. |
