EFFECT OF FUNGI ON THE OXIDATION‐REDUCTION POTENTIALS OF LIQUID CULTURE MEDIA

Abstract

BIOLOGICAL OXIDATIONS and reductions which deal with tlle energy relationships essential to all forms of life have been studied by many investigators, all aiming at an ultimate understanding of these complex processes. Since the release or building up of energy involves the transfer of electrons, it is possible to measure these phenomena in biological systems by oxidation-reduction indicators or electrical apparatus in which electron transfers result in color changes or in the building up of an electrical charge at suitable electrodes. Investigations on the effects of plants on oxidationreductioln potentials (Eh) have been confined chiefly to bacteria and yeasts. Hewitt (1933) has given an extensive review of the effects of bacteria on electrode potentials, listing over 65 references dealing with this suibject. Many. more results have been reported on oxidation-reduction phenomena in relation to bacterial metabolism since Hewitt's report was published. Potter (1912) showed that yeast cells produced redulcing conditions in their surrounding medium. Using both indicators and electrical methods of measuring Elh, Cannan, Cohen, and Clark (1926) followed the potential changes produced by yeast cells suspended in buffer solutions. They concluded that yeast cells produce hydrogen donators which reduce tthe media and result in the lowering of the oxidation-reduction potentials. Aubel, Aubertin, and Genevois (1929) showed that anaerobic yeast cultures had an Eh of about 160 to 200 millivolts. In a study of the relation of metabolic processes to the oxidation-reduction potentials, Kluyver and Hoogerheide (1934) found that anaerobic fermentation began at an Eh of about 90 millivolts while aerobic fermentation began at a potential of about 160-250 millivolts. They found it possible to determine the dominant type of metabolism (i.e., respiration or fermentation) carried on in a yeast culture by observing the oxidation-reduction potential. In a recent report by Tang and Lin (1936) the results are given of an investigation on the effects of the unicellular algae Chlorella vulgaris and C. pyrenoidosa on the oxidation-reduction potentials and pH of a synthetic nutrient solution. As shown with bacteria and yeasts, these algae also lowered the Eh of the media when respiration was the dominant type of metabolism-i.e., when the potentials were measured in darkness. In the presence of light, when presumably photosynthesis was the dominant process, the El values became more positive.