Spontaneous mutations changing the raffinose metabolism of Lactobacillus plantarum

Lactobacillus plantarum ATCC 8014 grew poorly on raffinose agar plates, but large mutant colonies appeared in high frequency from a thin film of background growth. The alpha-galactosidase and beta-galactosidase activities of L. plantarum ATCC 8014 and a mutant strain were studied in static cultures and pH-controlled fermenter cultures. Both alpha-galactosidase and beta-galactosidase production were inducible in the parental strain; the induction was not needed in the mutant. The alpha-galactosidase activity of both strains was repressed by glucose but not by alpha-methyl-D-glucoside. The mutant phenomenon might be an obstacle in connection to traditional Lactobacillus identification by means of carbohydrate fermentation.