Plasmid-encoded functions of ropy lactic acid streptococcal strains from Scandinavian fermented milk.

Ropy Streptococcus (Lactococcus) cremoris strains isolated from a ropy Swedish sour milk ("longfil") and a ropy Finnish milk product ("Viili") were screened for their plasmid-encoded functions. Curing experiments strongly indicated that the ropy phenotype was linked to a 17-Md plasmid in the Swedish strains and to a 30 Md plasmid in the Finnish strains. Comparative restriction endonuclease analysis and DNA/DNA-hybridization studies revelated that plasmids from both strain families shared homologous DNA regions. Though be Swedish ropy strains harbored a conjugative 45-Md lactose plasmid, no cotransfer of the 17 Md plasmid occurred.