Genetic Homology and Attempted Transformation among Certain Lactic Streptococci

Abstract

Evidence is presented which further substantiates earlier contentions that the lactic streptococci responsible for the malty defect in milk are very closely related to Streptococcus lactis. The average denaturation temperature (Tm) of deoxyribonucleic acid (DNA) from malty strains examined was 85.06C, the mean per cent guanine + cytosine (GC) was 38.43. The mean Tm of DNA from nonmalty strains was 85.15C, the corresponding mean for per cent GC was 38.62. The mean Tm for all strains examined was 85.10C, the mean GC composition was 38.54%. Homogeneity is evident since all strains examined exhibited similar to identical DNA base compositions. Results from DNA-RNA hybridization experiments indicate closely related DNA compositions and, therefore, a degree of genetic homology among the organisms investigated. However, under the experimental conditions employed, all attempts to affect transfer of the malty character and streptomycin-resistance to selected recipient cells were unsuccessful.