QUANTITATIVE STUDIES ON SOME MYCOBACTERIAL PHAGE-HOST SYSTEMS

Abstract

Use was made of standard bacteriophage techniques to study several mycobacterial phage-host systems. The original phage suspension, D29, gave 3 plaque-type variants when plated by soft-agar overlay technique on Mycobacterium butyricum. These were purified and found to breed true. Experiments were performed to determine optimal plating conditions for 2 of the variants, D29L (large plaque) and D29S (small plaque). Methods for propagation and concentration of the 2 phages were studied. The 2 phages were found morphologically and serologically (neutralization) similar, but they differed with respect to adsorption. Phages D29L and D29S appear heterogeneous with respect to adsorption on the hosts studied (slow and fast adsorbers). In suspensions of D29L the fraction of slow adsorbers appears smaller than that of D29S. About 0.5 of D29S and about 0.9 of D29L adsorbed to their hosts fail to produce plaques (abortion). Calcium supplement of 5 x 10-4 [image] or higher in adsorption mixtures (D29S- M. ranae) prevents abortion. One-step growth experiments (D29S-M. ranae) in broth gave successive cycles of phage growth, whereas in Tween-broth a one-step cycle was isolated. The minimal latent period is 85-90 min; the rise period is about 45 minutes; and the average burst size is about 18. Neutralization of either phage by homologous or heterologous antisera was exponential. The 2 phages were indistinguishable in these tests. The antisera had k values of about 25. Electron micrographs show the 2 phages to be morphologically similar.