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Symbiosis Among Lactic Streptococci

Department of Food Science and Processing, North Carolina State College, Raleigh

ABSTRACT

Combination of isolates from mixed-strain lactic streptococcus cultures showed different interactions when grown in milk. The effects varied from marked stimulation to inhibition. The interaction between strains could not be predicted from the growth rate of the individual isolates, or their cultural properties on an agar medium designed to measure acid production by bacterial colonies.

The marked acceleration of a faster culture by a slower one was obtained by using filtrate from a milk culture of the slower organism as well as by the organism itself. The active components were present nearly optimally in the slow culture after only one day at 22 C, and 1% of this filtrate was sufficient to stimulate the faster strain. The active material in the filtrate was dialyzable through cellophane. Filtrate of the fast strain was only slightly active for the slow culture.

Activity of the filtrate from the slow culture was adsorbed on Amberlite IRC (H⁺) and eluted by a 4% solution of aqueous ammonia. The eluate was observed to contain all of the activity in the original filtrate. Part of the activity was destroyed by acid hydrolysis.