Conjugal transfer of bacteriophage resistance to prolate phages in Lactococcus lactis

Abstract

Conjugal transfer of lactose-fermenting ability (Lac + ) and lytic phage resistance (Lpr + ) was demonstrated in four matings between Lactococcus lactis ssp. lactis C2, phage resistant mutant donor strains C21, C23 and C26 and the C2 derivative LM2302 plasmid free recipient strain. Transconjugants were selected with Lac + Em r and/or St r phenotypes. Lac + was transferred from donor strains to Lac − Em r and r St r phage sensitive recipient strains at a frequency of 10 −6 to 10 −8 revealing that Lac + and subsequently Lpr + were transferred. Although clumping (Clu) effects with a subsequent high frequency transconjugation (Hft) have been observed before in related strains, it was not evident in this case. Phage assays with Argentine (ARG) and United States (US) phage revealed that recipient strains were Lpr − . Because the transconjugants had the same lytic pattern as the corresponding donor strain, it is apparent that the unselected Lpr + trait was cotransferred with the Lac + marker on a 45 kb plasmid. A significant reduction in bacteriophage adsorption and failures in plaque formations for the ARG and the US prolate phages in all Lpr + strains was also observed. These results suggest that the Lpr + trait is mobilized by conjugal transfer.