Vitamin Deficiency as One Explanation for Inhibition of Protozoan Growth by Conditioned Medium

Abstract

Accelerative effects of biologically conditioned casein-peptone medium, when added to fresh medium in proportions of 1-5 parts in 10, have been reported previously for Colpidium campylum. 1 Subsequently, it has been found that an increase in the proportion of conditioned medium induces inhibitory effects on the growth of Colpidium campylum and Glaucoma piriformis. ∗ Observations on the latter are presented below.

Series I and II. A culture filtrate was prepared from 96-day flask-cultures of G. piriformis in casein-peptone (Difco “tryptone”) medium containing KH₂PO₄ (1.0 g per 1). The cultures were filtered through paper (Whatman No. 12), as previously described by Hall and Loefer, 1 and the filtrate was divided into two portions. One portion (Series I) served as the control medium. To the other (Series II), the following growth-factors were added: Merck's thiamine hydrochloride (1 × 10^-6 g per cc), Merck's riboflavin (1 × 10^-7 g per cc), and S. M. A. Corporation's nicotinic acid amide (1 × 10^-7 g per cc). Each medium was tubed in 10 cc amounts and sterilized in the autoclave at 122° C for 20 minutes. All tubes received 0.5 cc inocula from a 3-day culture of G. piriformis in the basic medium. In both series, the initial pH was 6.9; initial count, 4,000 ciliates per cc. All cultures were incubated in darkness at 24°C, and counts were made at the indicated intervals (Fig, 1, A).

Series III and IV. The procedure was the same as above, except that 109-day flask-cultures were used as the source of the filtrate, and a 21-day stock culture was used for inoculation. Series III served as the control; in series IV, the medium received the 3 growth-factors. In both series, the initial count was 6,400 ciliates per cc; initial pH, 6.9.