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PubMed1984

Conjugative 40-megadalton plasmid in Streptococcus lactis subsp. diacetylactis DRC3 is associated with resistance to nisin and bacteriophage.

Streptococcus lactis subsp. diacetylactis DRC3 was examined for plasmid DNA and found to contain a previously unreported plasmid of 40 X 10(6) daltons. This plasmid, designated pNP40, was conjugally transferred to a plasmid-cured derivative of S. lactis C2. Transconjugants containing pNP40 acquired resistance to nisin produced by strains of S. lactis and to commercially available nisin when assay plates were incubated at 21, 32, and 37 degrees C. In addition, c2 phage growth was completely restricted in transconjugants containing pNP40 at 21 and 32 degrees C, but not at 37 degrees C. This result suggests that pNP40 may be coding for a temperature-sensitive enzyme that restricts phage growth at 21 and 32 degrees C, but not at 37 degrees C. Eight consecutive transfers of a transconjugant containing pNP40 in Elliker broth at 37 degrees C resulted in 100% loss of resistance to c2 phage when colonies were tested at 32 degrees C. These phage-sensitive isolates had lost pNP40 and had also become sensitive to nisin. This result suggests that pNP40 may also be thermosensitive in its replication. The finding of a phage resistance determinant located on a conjugative plasmid should prove useful in constructing phage-resistant variants for dairy fermentation processes.

Bacteriophages↗

PubMed1984

Phage Resistance in a Phage-Insensitive Strain of Streptococcus lactis: Temperature-Dependent Phage Development and Host-Controlled Phage Replication.

Streptococcus lactis ME2 is a dairy starter strain that is insensitive to a variety of phage, including phi18. The efficiency of plating of phi18 on ME2 and N1 could be increased from <1 x 10 to 5.0 x 10 and from 7.6 x 10 to 2.1 x 10, respectively, when the host strains were subcultured at 40 degrees C before plating the phage and the phage assay plates were incubated at 40 degrees C. Host-dependent replication was demonstrated in N1 at 30 degrees C and in N1 and ME2 at 40 degrees C, suggesting the operation of a temperature-sensitive restriction and modification system in ME2 and N1. The increased sensitivity of ME2 and N1 to phi18 at 40 degrees C was also demonstrated by lysis of broth cultures and increased plaque size. ME2 grown at 40 degrees C showed an increased ability to adsorb phi18, indicating a second target for temperature-dependent phage sensitivity in ME2. Challenge of N1 with a phi18 preparation that had been previously modified for growth on N1 indicated that at 40 degrees C phage development was characterized by a shorter latent period and larger burst size than at 30 degrees C. The evidence presented suggests that the high degree of phage insensitivity expressed by ME2 consists of a variety of temperature-sensitive mechanisms, including (i) the prevention of phage adsorption, (ii) host-controlled restriction of phage, and (iii) suppression of phage development. At 30 degrees C these factors appear to act cooperatively to prevent the successful emergence of lytic phage active against S. lactis ME2.

Journal Article↗

PubMed1979

Lactose metabolism in Streptococcus lactis: phosphorylation of galactose and glucose moieties in vivo.

Starved cells of Streptococcus lactis ML3 grown previously on lactose, galactose, or maltose were devoid of adenosine 5'-triphosphate contained only three glycolytic intermediates: 3-phosphoglycerate, 2-phosphoglycerate, and phosphoenolpyruvate (PEP). The three metabolites (total concentration, ca 40 mM) served as the intracellular PEP potential for sugar transport via PEP-dependent phosphotransferase systems. When accumulation of [14C]lactose by iodoacetate-inhibited starved cells was abolished within 1 s of commencement of transport, a phosphorylated disaccharide was identified by autoradiography. The compound was isolated by ion-exchange (borate) chromatography, and enzymatic analysis showed that the derivative was 6-phosphoryl-O-beta-D-galactopyranosyl (1 leads to 4')-alpha-D-glucopyranose (lactose 6-phosphate). After maximum lactose uptake (ca. 15 mM in 15 s) the cells were collected by membrane filtration and extracted with trichloroacetic acid. Neither free nor phosphorylated lactose was detected in cell extracts, but enzymatic analysis revealed high levels of galactose 6-phosphate and glucose 6-phosphate. The starved organisms rapidly accumulated glucose, 2-deoxy-D-glucose, methyl-beta-D-thiogalactopyranoside, and o-nitrophenyl-beta-D-galactopyranoside in phosphorylated form to intracellular concentrations of 32, 32, 42, and 38.5 mM, respectively. In contrast, maximum accumulation of lactose (ca. 15 mM) was only 40 to 50% that of the monosaccharides. From the stoichiometry of PEP-dependent lactose transport and the results of enzymatic analysis, it was concluded that (i) ca. 60% of the PEP potential was utilized via the lactose phosphotransferase system for phosphorylation of the galactosyl moiety of the disaccharide, and (ii) the residual potential (ca. 40%) was consumed during phosphorylation of the glucose moiety.

Biological Transport, Active↗

PubMed1982

Distinct galactose phosphoenolpyruvate-dependent phosphotransferase system in Streptococcus lactis.

Lactose-negative (Lac-) mutants were isolated from a variant of Streptococcus lactis C2 in which the lactose plasmid had become integrated into the chromosome. These mutants retained their parental growth characteristics on galactose (Lac- Gal+). This is in contrast to the Lac- variants obtained when the lactose plasmid is lost from S. lactis, which results in a slower growth rate on galactose (Lac- Gal+). The Lac- Gal+ mutants were defective in [14C]thiomethyl-beta-D-galactopyranoside accumulation, suggesting a defect in the lactose phosphoenolpyruvate-dependent phosphotransferase system, but still possessed the ability to form galactose-1-phosphate and galactose-6-phosphate from galactose in a ratio similar to that observed from the parental strain. The Lac- Gald variant formed only galactose-1-phosphate. The results imply that galactose is not translocated via the lactose phosphoenolpyruvate-dependent phosphotransferase system, but rather by a specific galactose phosphoenolpyruvate-dependent phosphotransferase system for which the genetic locus is also found on the lactose plasmid in S. lactis.

Disaccharides↗

PubMedDate not supplied

[Ultrastructural features of Rhodococcus rubropertinctus and Streptococcus lactis dissociants].

Three Rhodococcus rubropertinctus dissociants (R, S and M) and two Streptococcus lactis dissociants (R and S) were compared using the electron microscopy method of negative contrasting. The cell wall of R.rubropertinctus dissociants had a thickness of 40 nm (R), 30 nm (S) and 20 nm (M). The cell wall of S. lactis dissociants was 35-55 nm (R) and 25-30 nm (S) thick. 1.5-2-fold variations in the thickness of cell walls could account for the different resistance of the dissociants against the action of such external factors as dehydration, antibiotics, UV, elevated NaCl concentrations, etc.

Lactococcus lactis↗

PubMedDate not supplied

[Joint culturing of Streptococcus lactis, strain MGU with Proteus vulgaris and Bacillus mesentericus].

Nisin synthesis by Streptococcus lactis, strain MGU, grown as a combined culture together with Proteus vulgaris and Bacillus mesentericus under stationary conditions or with stirring does not depend on the quantity of inoculated associated cells. Nisin synthesis in the combined culture drops down by 10-20% at the initial pH 7.5 of the growth medium which is unfavourable for S. lactis producing nisin. The level of nisin biosynthesis does not rise when the pH of the medium is adjusted (either naturally or artificially) to 6.6-6.8 in the presence of glucose and yeast autolysate. S. lactis inhibits the growth of B. mesentericus when grown together with it whereas P. vulgaris inhibits the growth of S. lactis in their combined culture.

Bacillus↗

PubMed1981

The importance of inorganic phosphate in regulation of energy metabolism of Streptococcus lactis.

This paper is concerned with the control of glycolysis in nongrowing Streptococcus lactis 7962. Changes were measured in the concentrations of glycolytic intermediates, intracellular inorganic phosphate (Pi), and adenine nucleotides following addition of glucose to cells that were in a starved condition. We find that intracellular Pi is a major factor in the control of glycolysis. In starved cells, the intracellular Pi concentration is high, greater than 40 mM. The large phosphoenolpyruvate pool that exists in starved cells can be explained as a result of inhibition of pyruvate kinase by the high concentration of Pi. On the other hand, in cells that are metabolizing glucose at a steady state rate, the cellular Pi concentration is low and pyruvate kinase is active. Upon depletion of glucose from the medium, the metabolite concentrations return to the values originally found in the starved state. This glucose depletion raises the intracellular Pi which again leads to inhibition of pyruvate kinase and the consequent buildup of the P-enolpyruvate pool.

Energy Metabolism↗

PubMed1984

Method for Growth and Purification of Bacteriophage 643 on Streptococcus lactis ML3.

The yield of bacteriophage 643 was increased by infecting cultures of Streptococcus lactis ML3 in late-log phase growth, harvesting the infected cells, and suspending them in fresh, phosphate-buffered minimal medium. The cells lysed after this treatment and produced high titers of bacteriophage. The phage particles were dissociated from debris by 2 M NaCl and purified by differential and CsCl band centrifugation.

Journal Article↗

PubMedDate not supplied

[Influence of pH on nisin production by Streptococcus lactis cultures].

The pH effect on the nisine biosynthesis during the cultivation of Streptococcus lactis was studied at pH 5,8 6,7 and 7,2. The pH maintenance at the specified level did not stimulate the growth of Str. lactis, did not increase the total yield of nisine and did not produce a significant effect on the level or cellular nisine. This indicates an important physiological difference between the culture-nisine producer described by Hirsh and our culture Str. lactis, str. Moscow University.

Hydrogen-Ion Concentration↗

PubMed1977

Growth requirements and the effect of organic components of the synthetic medium on the biosynthesis of the antibiotic nisin in Streptococcus lactis strain.

A synthetic medium SM-3 has been elaborated for growth of Streptococcus lactis strain 51, which contains the minimal number of organic components required for the growth of this strain and nisin production. This medium contains 9 amino acids, 4 vitamins from B group, glucose and mineral salts. Addition of biotin to the medium stimulated the growth of the strain, while the addition of purines and/or pyrimidines had no effect. Hitherto biotin has been considered to be necessary for the growth of S. lactis and purines and pyrimidines were believed to stimulate the growth of these bacteria. In strain 51 the minimal requirements for growth were also the minimal requirements for nisin biosynthesis. Strain 51 produced 3-4 times less nisin in medium SM-3 than in a complex medium. The addition of one of four amino acids (serine, proline, cysteine or cystine) to SM-3 medium increased the amount of antibiotic produced. The addition of all four amino acids simultaneously, caused formation of nisin amounts similar to those produced in complex medium.

Amino Acids↗

PubMed1986

[Nisin biosynthesis during the joint cultivation of Streptococcus lactis strain MGU and yeasts].

In simultaneous inoculation of the medium for nisin biosynthesis with Streptococcus lactis (strain MSU) and yeasts such as Rhodotorula colostri, Zigowilliopsis californicus, Hansenuia anomala, Saccharomyces ludvigii, Kluyveromyces lactis and Endomyces magnusi the quantitative ratio of the inoculates in the mixed cultures is not in principle important for the antibiotic synthesis by the Streptococcus. When 6-, 12-, 18- and 24-hour inoculates of the yeasts were added simultaneously to 3-, 6-, 9-, 12- and 18-hour cultures of S. lactis biosynthesis of nisin was at the control level. The fractional composition of the fermentation broth of the above yeast species had no significant effect on biosynthesis of nisin.

Culture Media↗

PubMed1974

Pyruvate kinase of Streptococcus lactis.

The kinetic properties of pyruvate kinase (ATP:pyruvate-phosphotransferase, EC 2.7.1.40) from Streptococcus lactis have been investigated. Positive homotropic kinetics were observed with phosphoenolpyruvate and adenosine 5'-diphosphate, resulting in a sigmoid relationship between reaction velocity and substrate concentrations. This relationship was abolished with an excess of the heterotropic effector fructose-1,6-diphosphate, giving a typical Michaelis-Menten relationship. Increasing the concentration of fructose-1,6-diphosphate increased the apparent V(max) values and decreased the K(m) values for both substrates. Catalysis by pyruvate kinase proceeded optimally at pH 6.9 to 7.5 and was markedly inhibited by inorganic phosphate and sulfate ions. Under certain conditions adenosine 5'-triphosphate also caused inhibition. The K(m) values for phosphoenolpyruvate and adenosine 5'-diphosphate in the presence of 2 mM fructose-1,6-diphosphate were 0.17 mM and 1 mM, respectively. The concentration of fructose-1,6-diphosphate giving one-half maximal velocity with 2 mM phosphoenolpyruvate and 5 mM adenosine 5'-diphosphate was 0.07 mM. The intracellular concentrations of these metabolites (0.8 mM phosphoenolpyruvate, 2.4 mM adenosine 5'-diphosphate, and 18 mM fructose-1,6-diphosphate) suggest that the pyruvate kinase in S. lactis approaches maximal activity in exponentially growing cells. The role of pyruvate kinase in the regulation of the glycolytic pathway in lactic streptococci is discussed.

Adenosine Diphosphate↗

PubMed1977

Phosphoenolpyruvate and 2-phosphoglycerate: endogenous energy source(s) for sugar accumulation by starved cells of Streptococcus lactis.

In the absence of an exogenous energy source, galactose-grown cells of Streptococcus lactis ML3 rapidly accumulated thiomethyl-beta-D-galactopyranoside (TMG) and 2-deoxyglucose to intracellular concentrations of 40 to 50 mM. Starved cells maintained the capacity for TMG uptake for many hours, and accumulation of the beta-galactoside was insensitive to proton-conducting ionophores (tetrachlorosalicylanilide and carbonylcyanide-m-chlorophenyl hydrazone) and sulfydryl group reagents including iodoacetate and N-ethylmaleimide. Fluorimetric analysis of glycolytic intermediates in extracts prepared from starved cells revealed (a) high intracellular levels of phosphoenolpyruvate (13 mM; PEP) and 2-phosphoglycerate (approximately 39 mM; 2-PG), but an absence of other metabolites including glucose 6-phosphate, fructose 6-phosphate, fructose 1,6-diphosphate, and triosephosphates. The following criteria showed PEP (and 2-PG) to be the endogenous energy source for TMG accumulation by the phosphotransferase system: the intracellular concentrations of PEP and 2-PG decreased with concomitant uptake of TMG, and a close correlation was observed between maximum accumulation of the beta-galactoside and the total available concentration of the two intermediates; TMG accumulated as an anionic derivative, which after extraction and incubation with alkaline phosphatase (EC 3.1.3.1) formed the original analogue; fluoride inhibition of 2-phospho-D-glycerate hydrolyase (EC 4.2.1.11) prevented the conversion of 2-PG to PEP, and uptake of TMG by the starved cells was reduced by 80%; and the stoichiometric ratio [TMG] accumulated/[PEP] consumed was almost unity (0.93). In cells metabolizing glucose, all intermediates listed in (a) and (b) were found. Upon exhaustion of glucose from the medium, the metabolites in (b) were not longer detectable, while the intracellular concentrations of PEP and 2-PG increased to the levels previously observed in starved cells. The glycolytic intermediates in (b) are all in vitro heterotropic effectors of pyruvate kinase (adenosine 5'-triphosphate:pyruvate 2-O-phosphotransferase, EC 2.7.1.40) from S. lactis ML3. It is suggested that the capacity of starved cells to maintain high intracellular concentrations of PEP and 2-PG is a consequence of decreased in vivo activity of this key regulatory enzyme of glycolysis.

Biological Transport↗

PubMed1987

Dependence of Streptococcus lactis phosphate transport on internal phosphate concentration and internal pH.

Uptake of phosphate by Streptococcus lactis ML3 proceeds in the absence of a proton motive force, but requires the synthesis of ATP by either arginine or lactose metabolism. The appearance of free Pi internally in arginine-metabolizing cells corresponded quantitatively with the disappearance of extracellular phosphate. Phosphate transport was essentially unidirectional, and phosphate concentration gradients of up to 10(5) could be established. Substrate specificity studies of the transport system indicated no preference for either mono- or divalent phosphate anion. The activity of the phosphate transport system was affected by the intracellular Pi concentration by a feedback inhibition mechanism. Uncouplers and ionophores which dissipate the pH gradient across the cytoplasmic membrane inhibited phosphate transport at acidic but not at alkaline pH values, indicating that transport activity is regulated by the internal proton concentration. Phosphate uptake driven by arginine metabolism increased with the intracellular pH with a pKa of 7.3. Differences in transport activity with arginine and lactose as energy sources are discussed.

Adenosine Triphosphate↗

PubMed1987

Spontaneous release of temperate phage by relysogenized lactose-positive transductants of Streptococcus lactis C2.

Transduction for lactose-fermenting ability between the lactose-positive lysogen Streptococcus lactis LM0221 and plasmid-cured, prophage-cured, lactose-negative S. lactis LM2301 resulted in the appearance of lactose-positive transductants surrounded by a zone of clearing in the lactose-negative cell lawn. By using plaque assay procedures, the zones were shown to contain bacteriophage particles, and both spontaneous release and UV induction of prophage from these transductants were demonstrated. The DNA hybridization confirmed that LM2301 did not contain the prophage in its chromosome and that the zone-producing transductant KZ1 was relysogenized by the temperate bacteriophage. Further, a 4.35 Kb EcoRI digestion fragment appeared to contain the DNA sequences for integration into the chromosome and may provide a means for stabilizing cloned DNA by effecting chromosomal insertion in LM2301 derivatives. The selection of zone-producing lactose-positive transductants of LM2301 provided a means for detecting strains relysogenized by the temperate phage induced from LM0221.

Bacteriophages↗

PubMed1987

[IR spectrophotometric study of a mixed culture of Streptococcus lactis, strain MSU, and Rhodotorula colostri with agitation of the medium].

Physiological aspects of Streptococcus lactis, strain MSU development in mixed culture with Rhodotorula colostri were studied in connection with nisin biosynthesis. By the IR spectra the average content of the main components in the monoculture cells of S. lactis and its association with the yeast in the stationary growth phase was the following by dry weight: 54-58 per cent of protein, 14-16 per cent of nucleic acids, 26-28 per cent of carbohydrates and 3-5 per cent of lipids. Glucose and nitrogen in the fermentation broth were consumed completely. A significant quantity of KH2PO4 remained in the fermentation broth. Lactic acid excretion was observed. S. lactis, strain MSU was the leading component of the association under the studied cultivation conditions because just its IR spectra dominated in the spectra of the mixed culture.

Lactococcus lactis↗

PubMed1983

Characterization of Phage-Sensitive Mutants from a Phage-Insensitive Strain of Streptococcus lactis: Evidence for a Plasmid Determinant that Prevents Phage Adsorption.

A phage-insensitive strain of Streptococcus lactis, designated ME2, was used as a prototype strain for the study of mechanisms and genetics of phage resistance in the lactic streptococci. Mutants sensitive to a Streptococcus cremoris phage, varphi18, were isolated at a level of 17% from cultures of ME2 after sequential transfer at 30 degrees C. Phage-sensitive mutants of ME2 were not fully permissive to varphi18. The efficiency of plating of varphi18 on the mutants was 5 x 10 as compared with <10 for varphi18 on ME2. Further characterization of the mutants showed that they efficiently adsorbed varphi18 at levels of >99.8%, whereas ME2 adsorbed only 20 to 40% of varphi18. These results suggest that increased phage susceptibility of the mutants may result from the loss of a mechanism that inhibits phage adsorption. Moreover, the high frequency of spontaneous mutation in ME2 indicates the involvement of an unstable genetic determinant in this phage defense mechanism. ME2 was shown to possess 13 plasmids ranging in size from 1.6 to 34 megadaltons. Of 40 mutants examined that had increased efficiencies of plating, all were missing a 30-megadalton plasmid, pME0030. These data suggest that pME0030 codes for a function that prevents phage adsorption. Further phenotypic characterization of the phage-sensitive mutants showed that some mutants were deficient in the ability to ferment lactose (Lac) and hydrolyze milk proteins (Prt). However, the Lac and Prt phenotype segregated independently of the phage-sensitivity phenotype. One phage-sensitive adsorption mutant, designated N1, was tested for susceptibility to 14 different phages. N1 showed increased capacity to adsorb 4 and to replicate 2 of these 14 phages, thereby indicating a phage resistance mechanism in ME2 that generalizes to phage interactions other than the specific varphi18-ME2 phage-host interaction. These data provide evidence for a unique plasmid-linked phage defense mechanism in phage-insensitive strains of lactic streptococci.

Journal Article↗

PubMed1979

Plasmid Profiles of Lactose-Negative and Proteinase-Deficient Mutants of Streptococcus lactis C10, ML(3), and M18.

Lactose- and proteinase-negative (Lac Prt) mutants of Streptococcus lactis C10, ML3, and M18 were isolated after treatment with ethidium bromide. The Lac Prt mutants of C10 were missing a 40-megadalton plasmid. A 33-megadalton plasmid was absent in the ML3 mutants, and the M18 variants lacked a 45-megadalton plasmid. The results suggest a linkage of these metabolic traits to the respective plasmids. The possible complexity of the interrelationship between lactose metabolism and proteinase activity is presented.

Journal Article↗