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Plasmid Linkage of Proteinase and Lactose Fermentation in Streptococcus lactis NCDO 1404¹

Department of Microbiology, Oregon State University, Corvallis 97331-3804

ABSTRACT

Streptococcus lactis NCDO 1404, a nisin producer, contained seven plasmid species with masses ranging from ap- proximately 1.8 to 45 megadaltons. Transfer in Ml 7 broth resulted in loss of the 45-megadalton plasmid with con- current impairment of growth in milk or on milk-based agar media, in spite of fast lactose fermentation. Growth at 41 C or protoplast regeneration were used for plasmid curing. Among seven partly-cured, lactose-negative derivatives, one retained the 45-megadalton plasmid and formed significantly larger colonies on milk-based agar media. These data indicated linkage of proteinase (positive) to the 45-mega-dalton plasmid. A 35-megadalton species was the only plasmid absent in all lactose- negative derivatives; this plasmid was present in Streptococcus lactis NCDO 1404 and in two lactose-positive de- rivatives. Linkage of lactose fermentation to the 35-megadalton plasmid was in- dicated. Streptococcus lactis NCDO 1404 and its derivatives produced four colony types on buffered, milk-based agar media containing pH indicators; the colony types corresponded to the four possible combinations of the proteinase-positive, and proteinase-negative, lactose-positive and lactose-negative phenotypes. All strains were capable of fast sucrose fermentation, including a nisin-negative derivative. Assignment of nisin production to a certain plasmid species could not be made.

¹ Technical Paper No. 7154, Oregon Agricultural Experiment Station.

² Technical Paper No. 7154, Oregon Agricultural Experiment Station.