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During studies on spontaneous loss of lactose metabolism inStreptococcus lactis C2, it was found that the lactose-negative (lac - ) mutants were also proteinase negative (prt - ). This pleiotropic effect was observed inS. diacetilactis 18-16, but not inS. cremoris B1. Thelac- prt- mutants fromS. lactis C2 were able to grow in milk, but no pH change or measurable protein breakdown occurred. When the milk was supplemented with glucose, a slow decline in pH occurred. Addition of a protein hydrolysate to milk did not stimulate acid production. When both supplements were added to milk, normal growth and pH change were obtained. When thelac- prt- mutant ofS. lactis C2 was transduced with the temperate phage from thelac+ prt+ parent culture, approximately equal numbers oflac+ prt- andlac+ prt+ transductants were obtained. When the spontaneouslac+ prt- strain ofS. lactis C2 was converted to alac- prt- derivative and transduced, similar results were obtained. The co-transduction of the lactose and proteinase markers suggest they are closely associated. The findings indicate that the transducing phage fromS. lactis C2 can be used to examine the causes of instability in both the lactose and proteinase enzyme systems of this organism.

Simultaneous Loss of Proteinase- and Lactose-Utilizing Enzyme Activities in Streptococcus lactis and Reversal of Loss by Transduction