GROWTH OF LACTIC-ACID BACTERIA AND BIFIDOBACTERIA ON LACTOSE AND LACTOSE-RELATED MONOSACCHARIDES, DISACCHARIDES AND TRISACCHARIDES AND CORRELATION WITH DISTRIBUTION OF BETA-GALACTOSIDASE AND PHOSPHO-BETA-GALACTOSIDASE

Spectrophotometric assays of beta-galactosidase (EC 3.2.1.23) and phos pho-beta-galactosidase (EC 3.2.1.85) activity were used to survey the lactose utilization pathways of lactic acid bacteria and bifidobacteri a. Beta-Galactosidase activity was found in all six genera represented (Lactococcus, Streptococcus, Leuconostoc, Lactobacillus, Pediococcus and Bifidobacterium) while phospho-beta-galactosidase was restricted t o the lactococci, two Lactobacillus and two Leuconostoc species. A num ber of strains of Lactococcus lactis, Lactobacillus casei and Leuconos toc spp. contained both enzymes. Enzyme activities varied when cells w ere grown on different sugars, but in general were low or absent for c ells grown on glucose compared with lactose. Two lactose-related compo unds, lactulose and galactosyl lactose, believed to be specific growth factors for bifidobacteria, supported growth amongst a wide range of lactic acid bacteria in addition to bifidobacteria. Growth on galactos yl lactose was restricted to some but not all strains containing beta- galactosidase, implying that the presence of beta-galactosidase is ins ufficient by itself to ensure utilization of galactosyl lactose. DNA f ragments that encoded the Lactococcus lactis subsp. cremoris phospho-b eta-galactosidase gene or the beta-galactosidase genes of Streptococcu s salivarius subsp. thermophilus or Lactobacillus delbrueckii subsp. b ulgaricus were isolated and used as probes in DNA-DNA hybridizations. Little or no hybridization was detected between these probes and plasm id or genomic DNA isolated froin heterologous species, despite the pre sence of the corresponding enzyme activity in the strains probed.