Bacteriophage infection of minicells

Abstract

Infection of minicells by bacteriophages results in the sequential appearance of phage encoded polypeptides in the absence of host cell syntheses. The polypeptides have been analyzed by polyacrylamide gel electrophoresis. Minicells produced by B. subtilis CU403divIVB1 have been infected by ϕ29, ϕ105, SP02, and minicells produced by E. coli DS410 by T5, λwt and λdg. Infection of minicells in the presence of chloramphenicol results in the synthesis of early mRNA. Removal of chloramphenicol and addition of rifampicin plus 14C-labelled amino acids results in a system permitting the identification of the polypeptides encoded by early mRNA. ϕ105 infection of minicells from a ϕ105 lysogenic B. subtilis minicell-producing strain results in a reduction in the amount and number of polypeptides synthesized as compared to ϕ105 infection of minicells from a nonlysogenic B. subtilis strain. A comparison of the polypeptides synthesized in minicells infected by λwt and λdg permits an identification of the polypeptides resulting from the expression of the E. coli genes carried by the λdg genome. Minicells can be purified in large amounts and maintain their activity when stored in tubes immersed in liquid nitrogen thus providing reproducible “in vivo” conditions for a large number of experiments.