Characteristics of phage abortion conferred in lactococci by the conjugal plasmid pTR2030

Abstract

The effect of pTR2030 on phage DNA injection, transfection, release of progeny phage, and cell death was evaluated for a number of lactococcal phages. Infection by prolate phage c2 and small isometric phage p2 of derivatives of Lactococcus lactis LM2301 with or without pTR2030, and infection by small isometric phage 𝜙31 of derivatives of L. lactis NCK202 with or without pTR2030 was studied. Phage DNA injection was not affected by pTR2030 when examined using blender-resistant-complex assays with 32P-labelled DNA or by observation of phage labelled with the fluorescent dye 4′,6-diamidino-2-phenylindole (DAPI). Successful transfection of hosts bearing pTR2030 indicated that the plasmid did not retard passage of naked phage DNA across the membrane. Infective-centre assays were used to determine whether progeny were released from phage-infected pTR2030 hosts that do not support plaque formation by small isometric phages. In all cases, pTR2030 reduced the number of infected hosts which generated viable phage. When progeny were released, the phage burst size was reduced. The data confirmed that pTR2030 interferes with development of prolate and small isometric phages in a similar manner via a classical abortive infection mechanism.