Mechanisms of Lactose Utilization by Lactic Acid Streptococci: Enzymatic and Genetic Analyses

Abstract

The apparent instability of ,B-galactosidase in toluene-treated cells or cell-free extracts of lactic streptococci is explained by the fact that these organisms do not contain the expected enzyme. Instead, various strains of Streptococcus lactis, S. cremoris, and S. diacetilactis were shown to hydrolyze o-nitrophenyl-f3-D-galactoside-6-phosphate (ONPG-6-P), indicating the presence of a different enzyme. In addition, lactose metabolism in S. lactis C2F was found to involve enzyme I (El), enzyme II (EII), factor III (FIII), and a heat-stable protein (HPr) of a phosphoenolpyruvate (PEP)-dependent phosphotransferase system analogous to that of Staphylococcus aureus. Mutants of S. lactis C2F, defective in lactose metabolism, possessed the phenotype lac-gal-. These strains were unable to accumulate 4{Cthiomethyl-,3-D-galactoside, to hydrolyze ONPG, or to utilize lactose -when grown in lactose or galactose broth. In addition, these mutants contained EI and HPr, but lacked EII, FIII, and the ability to hydrolyze ONPG-6-P. This suggested that the defect was in the phosphorylation step. Lactose-negative mutants of S. lactis 7962, a strain containing j3-galactosidase, could be separated into several classes, which indicated that this organism is not dependent upon the PEP-phosphotransferase system for lactose metabolism.on August 4, 2020 by guest

Regulation of sugar transport and metabolism in lactic acid bacteria

“…In 1969-1970 McKay and coworkers [18,19] first described the lac-PTS in the lactic strepto- cocci by in vitro complementation of soluble components (EI, HPr, EIII l"~) with a sugar-specific membrane fraction (Eli la~) prepared from S. lactis. However, it was not until 1977 following the discovery of the endogenous PEP-potential in starved cells of S. lactis [20] that the importance of PEP, and the highly efficient coupling of sugar transport to phosphorylation via the lac-PTS, were demonstrated in vivo.…”

Characterization of Lactose-Fermenting Revertants from Lactose-Negative Streptococcus lactis C2 Mutants

“…Group N streptococci use lactose via the phosphoenolpyruvate (PEP) transferase system (14,15) similar to that observed in Staphylococcus aureus (7,17). The mechanism of this reaction is described as follows, where HPr is a heat-stable soluble protein, EI (enzyme I) is a soluble protein, Ell-lac (enzyme II) is a lactosespecific membrane-bound component, FIII-lac (factor III) is a lactose-specific factor found in the soluble fraction of the cell, and P-fl-gal is phospho-f-D-galactosidase: PEP + HPr E P-HPr + pyruvate EI and HPr are constitutive components and are produced regardless of the type of carbohydrate present in the growth medium.…”

β-Galactosidase, phospho-β-galactosidase and phospho-β-glucosidase activities in lactobacilli strains isolated from human faeces

“…Three glycosidases, b-gal, P-b-gal and P-b-glc, take part in the fermentation of lactose. The distribution of b-gal and P-b-gal activities in various LAB have been reported (McKay et al 1970;Premi et al 1972) including reports from our laboratory (Sasaki et al 1993). However, there are no citations for the distribution of P-b-glc activity in LAB isolated from the human faeces.…”