β-Galactosidase of Streptococcus lactis

Abstract

3-galactosidase by several strains of Streptococcus lactis was induced by lactose. The rate of hydrolysis of o-nitrophenyl-,3-D-galactopyranoside was used to measure enzyme activity. The enzyme of all but one strain was unstable when whole cells were soIniCtreated or treated with toluene; the enzyme of one strain of S. lactis was stable to these treatments, which resulted in at least a fivefold increase in activity over that found in whole cells. The optimal assay conditions for toluene-treated cells of this strain involved incubation at 37 C in pH 7.0 sodium phosphate buffer. Lactose was the most effective inducer of enzyme synthesis. Methyl-3-D-thiogalactopyranoside, isopropyl-fl-D-thiogalactopyranoside, and galactose were also inducers of the enzyme, but were not as effective as lactose. Melibiose, maltose, and calcium lactobionate were poor inducers of enzyme synthesis. Exogenously supplied glucose repressed enzyme synthesis. The means of control of induced ,B-galactosidase synthesis in S. lactis was similar to that in Escherichia coli. added to a concentration of 0.002 g/ml. Buffer solutions. Cells were washed, suspended, and assayed in one of the following buffer solutions: 0.05 M sodium phosphate (pH 6.0 to 8.0), 0.05 M potassium phosphate (pH 7.0), 0.05 M tris (hydroxymethyl)aminomethane (Tris) (pH 7.0), 0.05 M Tris + 0.05 sodium chloride (pH 7.0), or 0.05 M Tris + 0.05 M sodium phosphate (pH 7.0). When indicated, MnCl2*4H20 was added to a concentration of 0.0004 M. Harvesting of cells. Culture samples were immediately chilled and centrifuged at 3,000 X g 937

Spray drying as a method for preparing concentrated cultures of Lactobacillus bulgaricus

“…Normal and dried-rehydrated samples (original concentration about 1 x lo9 cells m1-I) were centrifuged at 5000 g for 10 rnin at 4°C. The supernatant fluids (after filter sterilization) and cell pellets (resuspended in 20 ml of AM buffer) were used to measure P-galactosidase activity by the method described by Citti et al (1965).…”

“…Total activity of each sample was determined by permeabilizing the cells with toluene (Citti et al 1965) before the P-galactosidase assay. Total activity was considered as 100%.…”

Action of tributyltin on enzymes of four bacteria

“…For intact cells, one drop of toluene was added to 1 ml of cell suspension to increase the permeability of the cell envelope [24]. After the toluene treatment, ATPase activities in P. putida TBT-6, Pseudomonas sp.…”

“…The absorbance of the supernatant fluid was measured at 420 nm. One unit of activity is defined as 1 pmole of o-nitrophenol liberated per minute, which was determined from a standard curve of o-nitrophenol [24].…”

Looking backward and forward at the practical applications of genetic researches on lactic acid bacteria

“…The biochemical and genetic aspects of lactose metabolism in lactic streptococci has been thoroughly reviewed [116]. The principal system operating in these bacteria is the PEP lactose phosphotransferase system (PTS), though one strain, S. lactis 7962, relies on the/~-galactosidase system [117]. Both activities are present in some strains [118,119].…”