Effects of Culture Filtrates and Old Medium on Growth of the Giliate, Colpidium campylum

Abstract

Effects of protozoan metabolic products on growth of homologous species have been investigated by several workers. One view, based originally upon Woodruff's findings, predicates that waste products of a given species exert an inhibitory effect on growth of that species. The opposite view is represented by Dimitrowa's conclusion that growth of Paramecium caudatum is accelerated by small amounts of old culture fluid added to fresh cultures. Johnson and Hardin have observed no significant effects of old culture fluid on growth of P. multimicronucleata. Mast and Pace, however, have reported that old culture fluid in high concentration inhibits, whereas, in low concentration, it accelerates growth of Chilomonas paramecium. Preliminary observations, reported by Hall and Loefer, indicated that growth of Colpidium campylum in bacteria-free cultures is significantly accelerated by the addition of old culture filtrates to a peptone medium. Kidder has recently confirmed this accelerating effect of old culture fluid on growth of C. campylum, and has attributed it to a “biological conditioning” of the medium. In further study of this problem, the acceleration of growth by old culture filtrates has been compared with the effects produced by aged sterile medium added to fresh peptone solution. The results obtained in 8 experimental series are described graphically in Figs. 1 and 2. The following basic medium was used in all 8 series: casein-peptone (Difco “tryptone”), 10.0 g; KH2PO4, 2.0 g; glass-distilled water, 1.0 liter. However, 2 samples of tryptone were tested, one in Series I and II and the other in Series III-VIIL As indicated specifically for different series, old culture filtrate, filtered fresh medium, or filtered aged medium (uninoculated) was added to tubes containing fresh unfiltered peptone medium.