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PubMed1976

Characteristics and energy requirements of an alpha-aminoisobutyric acid transport system in Streptococcus lactis.

Galactose-grown cells of Streptococcus lactis ML3 acculated alpha-aminoisobutyric acid (AIB) by using energy derived from glycolysis and arginine catabolism. The transport system displayed low-affinity Michaelis-Menten saturation kinetics. Using galactose or arginine as energy sources, similar V max and K m values for AIB entry were obtained, but on prolonged incubation the intracellular steady-state concentration of AIB in cells metabolizing arginine was only 65 to 70% that attained by glycolyzing cells. Efflux of AIB FROM PRELOADED CElls was temperature dependent and exhibited the characteristics of a first-order reaction. The rate of AIB exit was accelerated two- to threefold in the presence of metabolizable energy sources. Metabolic inhibitors including p-chloromercuribenzoate, dinitrophenol, azide, arsentate, and N, N'-dicyclohexylcarbodiimide either prevented or greatly reduced AIB uptake. Fluoride, iodoacetate and N-ethylmaleimide abolished galactose-dependent, but not arginine-energized, AIB uptake. K+ and Rb+ reduced the steady-state intracellular AIB concentration by approximately 40%, and these cations also induced rapid efflux of solute from actively transporting cells. Equivalent concentrations (10 mM) of Na+, Li+, or NH4+ were much less inhibitory. The proton-conducting ionophores tetrachlorosalicylanilide and carbonylcyanide m-chlorophenlyhydrazone abolished uptake and induced AIB efflux even though glycolysis and arginine catabolism continued at 60 and 140%, respectively, of control rates. A proton motive force is most likely involved in the active transport of AIB, whereas data from efflux studies suggest that energy is coupled to AIB exit in cells of S. lactis ML3.

Aminoisobutyric Acids↗
PubMed1980

Galactose transport systems in Streptococcus lactis.

Galactose-grown cells of Streptococcus lactis ML3 have the capacity to transport the growth sugar by two separate systems: (i) the phosphoenolpyruvate-dependent phosphotransferase system and (ii) an adenosine 5'-triphosphate-energized permease system. Proton-conducting uncouplers (tetrachlorosalicylanilide and carbonyl cyanide-m-chlorophenyl hydrazone) inhibited galactose uptake by the permease system, but had no effect on phosphotransferase activity. Inhibition and efflux experiments conducted using beta-galactoside analogs showed that the galactose permease had a high affinity for galactose, methyl-beta-D-thiogalactopyranoside, and methyl-beta-D-galactopyranoside, but possessed little or no affinity for glucose and lactose. The spatial configurations of hydroxyl groups at C-2, C-4, and C-6 were structurally important in facilitating interaction between the carrier and the sugar analog. Iodoacetate had no inhibitory effect on accumulation of galactose, methyl-beta-D-thiogalactopyranoside, or lactose via the phosphotransferase system. However, after exposure of the cells to p-chloromercuribenzoate, phosphoenolpyruvate-dependent uptake of lactose and methyl-beta-D-thiogalactopyranoside were reduced by 75 and 100%, respectively, whereas galactose phosphotransferase activity remained unchanged. The independent kinetic analysis of each transport system was achieved by the selective generation of the appropriate energy source (adenosine 5'-triphosphate or phosphoenolpyruvate) in vivo. The maximum rates of galactose transport by the two systems were similar, but the permease system exhibited a 10-fold greater affinity for sugar than did the phosphotransferase system.

Adenosine Triphosphate↗
PubMed1984

Properties of a Streptococcus lactis strain that ferments lactose slowly.

Streptococcus lactis 7962, which ferments lactose slowly, has a lactose phosphoenolpyruvate-dependent phosphotransferase system and low phospho-beta-galactosidase activity, in addition to high beta-galactosidase activity. Lactose 6'-phosphate accumulated to a high concentration (greater than 100 mM) in cells growing on lactose. In contrast, lactic streptococci, which ferment lactose rapidly and use only the lactose-phosphotransferase system for uptake, contained high phospho-beta-galactosidase activity and low concentrations (0.9 to 1.6 mM) of lactose 6'-phosphate. It is concluded that rate-limiting phospho-beta-galactosidase activity is primarily responsible for defective lactose metabolism in S. lactis 7962.

Fermentation↗
PubMed1988

Plasmid-mediated reduced phage sensitivity in Streptococcus lactis KR5.

The phage insensitivity of Streptococcus lactis KR5 was evaluated for its possible linkage to plasmid DNA. This strain possessed plasmids of 40, 29, 26, 21, 16.5, 10.5, 7.8, and 1.5 Mdal. Plasmid curing using novobiocin resulted in derivatives with increased sensitivity to prolate-headed phage, suggesting the involvement of plasmid DNA in phage insensitivity. Transformation of S. lactis LM0230 protoplasts with the KR5 plasmid DNA pool produced transformants containing a plasmid of about 27 Mdal. These erythromycin-resistant transformants were lactose-positive phage-sensitive or were lactose-negative and exhibited a reduced sensitivity to phage. Agarose gel electrophoresis and restriction endonuclease digestion analysis showed the 27-Mdal plasmid band to be composed of two distinct plasmids of 26 Mdal (pBF61) and 29 Mdal (pBF62), which coded for reduced phage sensitivity and lactose-positive phenotypes, respectively. The mechanisms of reduced phage sensitivity encoded by pBF61 included a restriction/modification system and a mechanism that resulted in reduced plaque size independent of incubation temperature. These results further support the involvement of plasmid DNA in the mechanisms for reduced phage sensitivity in dairy streptococci.

Bacteriophages↗
PubMedDate not supplied

[A mutant of Streptococcus lactis with resistance to bacteriophages isolated in Argentina and the United States of America].

Streptococcus lactis and Streptococcus cremoris have an important role in the fermentation of milk during the manufacturing of lactic products. Bacteriophages are spread in the plant environment and they may infect the starters causing technical and economic problems to the dairy industry. It is now known that the usual methods of control are not completely safe against the proliferation of phages. It is necessary therefore to include resistant strains to the phages which infect the plant. This study introduces a simple and direct method to obtain spontaneous mutants which have performed clear resistance to a certain phage. The prolate (ARG) phages used in this work St11, St13 and St15 were isolated in Argentina, on S. lactis C2 while the prolate and isometric (AM) phages phi C2, D59-1, I16-1, and G72-1, F4-1, I37-1 respectively, were isolated in Cornell University. on the corresponding S. lactis strains except the phage D59-1 isolated on an S. cremoris strain. The propagation of phages was performed using M and M17 broth. The phage sensitivity was tested through spot test and overlay plaque plating method expressing the titre of phage suspension. as PFU/ml. In order to obtain spontaneous resistant mutants of S. lactis C2 to phage St15, and active culture of S. lactis C2 (sensitive) was spread on agar M plates, inoculated with drops of a suspension of phage St15 (10(8)PFU/ml) and incubated at 30 degrees C for 48 h. Colonies of mutants grown in the lytic areas caused by the phage were isolated and selected.(ABSTRACT TRUNCATED AT 250 WORDS)

Argentina↗
PubMed1976

Purification and properties of pyruvate kinase from Streptococcus lactis.

The pyruvate kinase (ATP: pyruvate 2-O-phosphotransferase, EC 2.7.1.40) of Streptococcus lactis C10 is activated by fructose 1,6-diphosphate (Fru-1,6-P2), activity being a sigmoidal function of activator concentration. The FDP0.5V (Fru-1,6-P2 concentration giving half-maximal velocity) is markedly increased in the presence of low concentrations of inorganic phosphate; 1 mM phosphate increases the FDP0.5V value 6-fold. Although the intracellular level of Fru-1,6-P2 (12-18 mM) in exponentially growing cells on the medium used is much greater than the FDP0.5V for pyruvate kinase (0.2 mM) as determined in triethanolamine-HCl buffer, a much higher Fru-1,6-P2 concentration may be required to activate the enzyme in vivo to overcome phosphate inhibition. Tris and maleate also inhibit the enzyme. At low concentrations of Fru-1,6-P2 (0.1 mM), reaction rate is a sigmoidal function of both phosphoenolpyruvate and adenosine diphosphate (ADP) concentrations; at near saturating concentrations of activator (1 mM) the response to varying ADP is hyperbolic while the response to varying phosphoenolpyruvate becomes much less sigmoidal. The affinity for both substrates (especially phosphoenolpyruvate) is also increased by increasing the concentration of Fru-1,6-P2. The affinity of the enzyme for guanosine disphosphate (GDP) is 12-13 times that for ADP under the assay conditions used. The Streptococcus lactis pyruvate kinase has a molecular weight of 240000 with a subunit molecular weight of 60000.

Adenosine Diphosphate↗
PubMed1964

EXTRACELLULAR PROTEINASE OF STREPTOCOCCUS LACTIS.

Williamson, W. T. (North Carolina State of the University of North Carolina, Raleigh), S. B. Tove, and M. L. Speck. Extracellular proteinase of Streptococcus lactis. J. Bacteriol. 87:49-53. 1964.-Streptococcus lactis was shown to produce an extracellular proteolytic enzyme(s). A 120-fold purification of the proteinase was obtained from the cell-free culture medium by ammonium sulfate fractionation, calcium phosphate gel treatment, and chromatography on diethylaminoethyl cellulose. Only 32% of the activity was destroyed by heating at 98 C for 1 hr. The requirement of free sulfhydryl groups for enzyme activity was indicated by inhibition with p-chloromercuric benzoate. Diisopropyl fluorophosphate did not inhibit the proteinase.

Benzoates↗
PubMed1963

FATTY ACID COMPOSITION OF LIPIDS FROM STREPTOCOCCUS CREMORIS AND STREPTOCOCCUS LACTIS VAR. MALTIGENES.

MacLeod, Patricia (University of Connecticut, Storrs) and Joseph P. Brown. Fatty acid composition of lipids from Streptococcus cremoris and Streptococcus lactis var. maltigenes. J. Bacteriol. 85:1056-1060. 1963.-A method for the extraction of lipids from bacterial cells, involving grinding in a ball mill, is described. Cells of Streptococcus lactis var. maltigenes and S. cremoris yielded 5.3 and 5.5%, respectively, of their dry cellular weights as lipid. The lipids of both organisms were separated into three fractions by thin-layer chromatography. Two of these fractions have been classified: one fraction containing phospho- and perhaps glycolipids and the other containing triglycerides. The unidentified fraction was probably either mono- or diglyceride in nature. The fatty acid composition of the total lipid as well as that of each of the separated lipid components from the two lactic strains were compared.

Chemical Phenomena↗