Metabolic Activity of the Bacterial Cell at Various Phases of the Population Cycle

Abstract

Colon-type bacteria were cultivated at 37[degree] C. in peptone water, lactose-peptone water, and in Dolloff synthetic medium (lactose and ammonium tartrate with a. trace of di-ammonium phosphate). During growth the cultures were aerated continuously with CO2-free, NH3-free air by which CO2 and NH3 produced by the bacteria were simultaneously removed from the medium for absorption and quantitative determination in subsequent train units. The aerated yields of CO2 and nH3 were collected during time periods known from previous growth-curve studies to represent, lag, logarithmic increase, peak stability, and death in the population cycle. At start and close of each production period the medium content of CO2 and NH3 was determined, pH reaction observed, and bacterial numbers counted. From the known total gas yields (aerated + medium increase), cell numbers, and time periods, rates per cell per hour for CO2 and NH3-nitrogen were calculated. Average rates obtained in plain peptone medium were for CO2 (all units mgm. X 10-11 per cell per hour), 1.3 during peak stability, 52 during logarithmic increase, and 42-99 during lag and growth acceleration; for NH3-N, 0.2, 4.5, and 10-24 for the respective periods. In lactose-peptone the CO2 rates were almost identical to those above (1.5. 54, 41-104), while the NH3-N rates were reduced in all phases (< 0.1, 0.5, 6-16). During a 1-day rest period ("initial stability") in Dolloff medium the CO2 and NH3-N rates were 2.9 and < 0.1. During a 1-day death phase induced in Dolloff solution by 1.5 M NaCl, rates were too small for accurate determination (0.2, 0.3) in that medium, but suggested autolysis rather than anabolism. A few exps. in peptone plus stimulating salt (0.1 M NaCl) appeared to reveal little salt effect on NH3 rates, but showed CO2 production rates increased in the lag period and reduced during the more rapid logarithmic increase promulgated by the salt. Conclusions drawn from the study are: The vastly greater rates of CO2 and NH3 production in the earlier growth phases than in stable populations give quantitative substantiation to the postulated existence of a phenomenon of physiological youth in bacterial cultures. Substitution of part of the peptone by a fermentable carbohydrate (lactose) does not alter the rate of CO2 production for any population phase, but causes definite reduction of NIL rates for all phases studied. The resulting rise in the molecular ratio of CO2/NH3-N in each phase gives quantitative measure of the Kendall "protein-sparing" phenomenon. It appears that differences in gas production revealed in ordinary fermentation tubes in presence or absence of sugar are not due to differences in production of CO2.