Comparison of Membrane Proteins from Lactic Streptococci by Gel Electrophoresis.

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Abstract
Slime forming Group N Streptococcus strains isolated from the Finnish fermented milk viili and nonslime forming control strains were characterized by comparing electrophoretic patterns of the membrane proteins. Cells of the nonslime forming S. cremoris Hki I and II, S. lactis Hki I and II and S. diacetilactis Hki, the slime forming S. cremoris Biotypes A (T5) and B (T1), and reference organism S. faecalis KTL were harvested in the late log phase of culture growth. Membranes were isolated by sonic treatment, lysozyme digestion and osmotic shock followed by digestion with DNase and RNase and incubation in sodium dodecyl sulfate-phosphate solution. The membrane proteins were separated in 5% polyacrylamide gels containing 0.1% of sodium dodecyl sulfate (SDS). The membrane proteins from nonslime forming and slime forming strains differ from each other in regard to the number of the polypeptides, the amount of corresponding proteins and the distribution of MW. The number of bands in the electrophoretic patterns of slime forming strains was smaller (10) than in those of nonslime forming strains (13-14). The slowly moving band 21 was the 1st minor band in slime forming strains. Three or 4 of the fastest bands, MW 15,000-41,200, were major bands in the nonslime forming strains. All but 2 or 3 bands in the slime forming strains were major bands. Proteins Nos. 17-21, MW 80,000-100,000, were common in nonslime forming strains and extremely rare in slime forming strains. S. faecalis, the reference organism from Group D, showed a group specific pattern where especially proteins with high MW were missing.