The Oxidation-Reduction Potential Requirements of a Non-Spore-Forming, Obligate Anaerobe

Abstract

A determination has been made of the apparent oxidation-reduction potential of the medium which just limits the growth of a strain of Bacteroides vulgatus, a non-spore-forming, obligate anaerobe. The organisms were inoculated into glucose nutrient broth contained in vessels provided with shiny platinum electrodes to measure the oxidation-reduction potential, and with glass electrodes to measure pH. Potentials were maintained at definite levels by controlling the composition of a N-air mixture which was bubbled through the culture. A small amt. of CO2 was found to be essential for growth of the organism. The CO2 was furnished with the gas mixture, which was passed through a saturated NaHC03 soln. before being led into the culture vessel. Potentials of +0.150 volt [plus or minus]0.010 at pH 6.6 completely inhibited growth; between +0.100 and 0.150 v. there was partial inhibition; below 0.100 v. there was uninhibited growth. Growth was measured by increase in turbidity and was always accompanied by the initiation of acid production. A greater proportion of O2 was necessary to maintain the potential level at a high positive value when growth was rapid than when growth was slow or when the medium was sterile. Fresh cultures of the anaerobe on glucose brain broth medium showed a high rate of O2 consumption which decreased rapidly with time. The findings are interpreted by postulating the existence in the anaerobic system of a necessary enzyme which is oxidatively inactivated by O2.