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PubMed1987

Restriction enzyme analysis of lactose and bacteriocin plasmids from Streptococcus lactis subsp. diacetylactis WM4 and cloning of BclI fragments coding for bacteriocin production.

The 131.1-kilobase (kb) bacteriocin production (Bac) plasmid pNP2 and the 63.6-kb lactose metabolism (Lac) plasmid pCS26, from Streptococcus lactis subsp. diacetylactis WM4, as well as pWN8, a 116.7-kb recombinant plasmid from a Lac+ transconjugant, were analyzed with restriction enzymes to determine the origin of pWN8. Plasmid pWN8 conferred a Lac+ Bac- phenotype, contained DNA derived from pCS26 and pNP2, and, like pNP2, exhibited self-transmissibility (Tra+). In cloning attempts, Bac+ transformant S. lactis KSH1 was isolated. The recombinant plasmid, pKSH1, contained three BclI fragments from pNP2. Bac- transformants which individually contained each of the three fragments were also identified. Comparison of restriction maps of pKSH1 and pNP2 revealed an 18.4-kb region common to both plasmids, involving two of the three BclI fragments. S. lactis KSH1 also exhibited greater inhibitory activity against the indicator strain S. diacetylactis 18-16 than did a strain containing the 131.1-kb Bac plasmid.

Bacteriocin Plasmids↗
PubMed1981

Proton motive force in growing Streptococcus lactis and Staphylococcus aureus cells under aerobic and anaerobic conditions.

Measurements of the electrochemical gradient of hydrogen ions, which gives rise to the proton motive force (PMF), were carried out with growing Streptococcus lactis and Staphylococcus aureus cells. The facultative anaerobe was chosen in order to compare the PMF of cells growing aerobically and anaerobically. It was expected that during aerobic growth the cells would have a higher PMF than during anaerobic growth, because the H+-translocating ATPase (BF0F1) operates in the direction of H+ influx and ATP synthesis during respiration, whereas under anaerobic conditions the BF0F1 hydrolyzes glycolytically generated ATP and establishes the proton gradient by extruding H+. The electrical component of the PMF, delta psi, and the chemical gradient of H+, delta pH, were measured with radiolabeled tetraphenylphosphonium and benzoate ions. In both S. lactis and S. aureus cells, the PMF was constant during the exponential phase of batch growth and decreased in the stationary phase. In both species of bacteria, the exponential-phase PMF was not affected by varying the growth rate by adding different sugars to the medium. The relative contributions of delta psi and delta pH to the PMF, however, depended on the pH of the medium. The internal pH of S. aureus was constant at pH 7.4 to 7.6 under all conditions of growth tested. Under aerobic conditions, the delta psi of exponential phase S. aureus remained fairly constant at 160 to 170 mV. Thus, the PMF was 250 to 270 mV in cells growing aerobically in media at pH 6 and progressively lower in media of higher pH, reaching 195 to 205 mV at pH 7. Under anaerobic conditions, the delta psi ranged from 100 to 120 mV in cells at pH 6.3 to 7, resulting in a PMF of 150 to 140 mV. Thus, the mode of energy metabolism (i.e., respiration versus fermentation) and the pH of the medium are the two important factors influencing the PMF of these gram-positive cells during growth.

Aerobiosis↗
PubMed1988

Transposition of the Streptococcus lactis ssp. lactis Z270 lactose plasmid to pVA797: demonstration of an insertion sequence and its relationship to an inverted repeat sequence isolated by self-annealing.

The lactose plasmid pUCL22 of the single plasmid strain Streptococcus lactis ssp. lactis Z270 was demonstrated to fuse with the heterologous conjugative plasmid pVA797. The fusion of pUCL22 with pVA797 occurred by recombination between a specific sequence of pUCL22 and different sites of pVA797. The cointegrates of pUCL22::pVA797 were unstable: in the absence of lactose selection, they segregated plasmids that corresponded to pVA797 enlarged by one sequence of 1.2 kb, common to all derivative plasmids. This resolution sequence (RS) was shown to originate in the 9.7 kb BstEII restriction fragment of pUCL22 and to duplicate during replicon fusion. In addition, after nuclease S1 treatment of pUCL22 DNA, a self-annealing sequence was isolated; the two copies of this inverted repeat (IR) sequence were located on the 18 kb BamHI segment of the plasmid. This latter sequence was distinct from the RS with which it hybridized weakly. The RS was responsible for the transposition of the entire lactose plasmid; the role of the IR remains to be elucidated.

Conjugation, Genetic↗
PubMed1984

Use of 31P nuclear magnetic resonance spectroscopy and 14C fluorography in studies of glycolysis and regulation of pyruvate kinase in Streptococcus lactis.

High-resolution 31P nuclear magnetic resonance spectroscopy and 14C fluorography have been used to identify and quantitate intermediates of the Embden-Meyerhof pathway in intact cells and cell extracts of Streptococcus lactis. Glycolysing cells contained high levels of fructose 1,6-bisphosphate (a positive effector of pyruvate kinase) but comparatively low concentrations of other glycolytic metabolites. By contrast, starved organisms contained only high levels of 3-phosphoglycerate, 2-phosphoglycerate, and phosphoenolpyruvate. The concentration of Pi (a negative effector of pyruvate kinase) in starved cells was fourfold greater than that maintained by glycolysing cells. The following result suggest that retention of the phosphoenolpyruvate pool by starved cells is a consequence of Pi-mediated inhibition of pyruvate kinase: the increase in the phosphoenolpyruvate pool (and Pi) preceded depletion of fructose 1,6-bisphosphate, and reduction in intracellular Pi (by a maltose-plus-arginine phosphate trap) caused the restoration of pyruvate kinase activity in starved cells. Time course studies showed that Pi was conserved by formation of fructose 1,6-bisphosphate during glycolysis. Conversely, during starvation high levels of Pi were generated concomitant with depletion of intracellular fructose 1,6-bisphosphate. The concentrations of Pi and fructose 1,6-bisphosphate present in starved and glycolysing cells of S. lactis varied inversely. The activity of pyruvate kinase in the growing cell may be modulated by the relative concentrations of the two antagonistic effectors.

Carbon Radioisotopes↗
PubMed1987

Biosynthesis and stereochemical configuration of N5-(1-carboxyethyl)ornithine. An unusual amino acid produced by Streptococcus lactis.

In a recent communication (Thompson, J., Curtis, M. A., and Miller, S.P.F. (1986) J. Bacteriol. 167, 522-529) we described the purification and characterization of N5-(1-carboxyethyl)ornithine from cells of Streptococcus lactis 133. This unusual amino acid has not previously been found in nature. Radiotracer experiments presented here reveal that exogenous [14C]ornithine serves as the precursor for biosynthesis of [14C]arginine, [14C]N5-(1-carboxyethyl)ornithine, and [14C]N5-acetylornithine by cells of S. lactis K1 during growth in a defined medium lacking arginine. In the absence of both arginine and ornithine, cells of S. lactis K1 can also generate intracellular [14C]N5-(1-carboxyethyl)ornithine from exogenous [14C]glutamic acid. Previously we showed that the properties of N5-(1-carboxyethyl)ornithine prepared from S. lactis were identical to one of the two diastereomers [2S, 7S) or (2S, 7R] present in a synthetic preparation of (2S, 7RS)-N5-(1-carboxyethyl)ornithine. The two diastereomers have now been unambiguously synthesized by an Abderhalden-Haase condensation between (2S)-N2-t-butoxycarbonyl-ornithine and the chiral (2S)-, and (2R)-bromopropionates. By 13C-NMR spectroscopy it has been established that the preparation from S. lactis is exclusively (2S, 7S)-N5-(1-carboxyethyl)ornithine. has been demonstrated in a cell-free extract of S. lactis 133. The requirements for ornithine, pyruvic acid, and NAD(P)H suggest that biosynthesis of N5-(1-carboxyethyl)ornithine occurs via a reductive condensation mechanism. A general survey revealed that N5-(1-carboxyethyl)ornithine was produced only by certain strains of Group N streptococci. These findings may indicate a plasmid locus for the gene(s) encoding the enzyme(s) for N5-(1-carboxyethyl)ornithine biosynthesis.

Carbon Radioisotopes↗
PubMed1982

Restriction endonuclease analysis of the lactose plasmid in Streptococcus lactis ML3 and two recombinant lactose plasmids.

We investigated the molecular relationship between the 60-megadalton (Mdal) recombinant lactose plasmids in ML 3 x LM2301 lactose-positive (Lac+) transconjugants and the genetic material of Streptococcus lactis ML3. Lactose metabolism is linked to the 33-Mdal plasmid pSK08 in ML3, and the recipient LM2301 is cured of plasmid DNA. The plasmids were analyzed with a series of restriction enzymes. We found that the 60-Mdal plasmids of Lac+ transconjugants contained pSK08 DNA, but were not simply dimers of pSK08. The 60-Mdal plasmids contained a segment of DNA not apparent in pSK08. The restriction patterns of the 60-Mdal plasmid in a Lac+ nonclumping transconjugant and that in a Lac+ clumping transconjugant were different. This suggested that there was a molecular differences between these two recombinant plasmids. We conclude that the segment of DNA in the 60-Mdal plasmids that was not present in pSK08 was the proposed transfer factor responsible for cell aggregation and high-frequency conjugation.

Base Sequence↗
PubMed1988

Viability and metabolic capability are maintained by Escherichia coli, Pseudomonas aeruginosa, and Streptococcus lactis at very low adenylate energy charge.

Metabolic regulation by nucleotides has been examined in several bacteria within the context of the adenylate energy charge (EC) concept. The ECs of bacteria capable of only fermentative metabolism (Streptococcus lactis and the ATPase-less mutant Escherichia coli AN718) fell to less than 0.2 under carbon-limiting conditions, but the bacteria were able to step up the EC to greater than 0.8 upon exposure to nutrient sugars. Similarly, nongrowing E. coli 25922, whose EC had been artificially lowered to less than 0.1 by the addition of the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP), was able to immediately step up the EC to 0.8 to 0.9 upon the addition of glucose but was unable to respond to respiratory substrates. The EC of respiring bacteria (E. coli 25922 and Pseudomonas aeruginosa 27853) fell to 0.3 to 0.4 under certain limiting growth conditions, but the bacteria also responded immediately when challenged with succinate to give EC values greater than 0.8. These bacteria could not step up the EC with respiratory substrates in the presence of CCCP. For all bacteria, the loss of the ability to step up the EC was attributable to the loss of nutrient transport function. Mixtures of viable and HOCl-killed E. coli 25922 were able to step up the EC in proportion to the fraction of surviving cells. The data indicate that nucleotide phosphorylation levels are not regulatory in nongrowing bacteria but that the EC step-up achievable upon nutrient addition may be an accurate index of viability.

Adenine Nucleotides↗
PubMed1988

Restriction and modification activities from Streptococcus lactis ME2 are encoded by a self-transmissible plasmid, pTN20, that forms cointegrates during mobilization of lactose-fermenting ability.

A self-transmissible (Tra+) plasmid encoding determinants for restriction and modification activities (R+/M+) from Streptococcus lactis ME2 was isolated and characterized. The 28-kilobase (kb) plasmid (pTN20) was detected in lactose-fermenting (Lac+) transconjugants generated from matings between S. lactis N1, and ME2 variant, and a plasmid-free recipient, S. lactis LM2301. The plaquing efficiencies of prolate- and small isometric-headed phages were reduced on transconjugants containing either pTN20 (R+/M+ Tra+) or 100-kb plasmids encoding Lac+, R+/M+, and Tra+. Lac+ transconjugants which harbored pTR1040 (Lac+) and pTN20 (R+/M+) were phenotypically R-/M- and transferred Lac+ at low frequency in subsequent matings to give rise to 100-kb R+/M+ plasmids. R+/M+ activities and high-frequency conjugal transfer ability were detected in Lac+ transconjugants that contained pTR1041 (Lac+) and pTN20 (R+/M+). No 100-kb R+/M+ plasmids were recovered after these matings, suggesting that pTR1041 was mobilized by pTN20 through a process that resembled plasmid donation. pTR1041 was identical to pTR1040 but contained an additional 3.3-kb DNA fragment. These data suggested that phenotypic expression of R+/M+ and Tra+ is affected by coresident Lac+ plasmids. Restriction enzyme analysis and hybridization reactions demonstrated that the 100-kb R+/M+ plasmid was formed by a cointegration event between pTR1040 (Lac+) and pTN20 (R+/M+ Tra+) during conjugal transfer via a conductive-type process. This is the first report that defines self-transmissible restriction and modification plasmids in the lactic streptococci.

Bacteriophages↗
PubMed1985

Intracellular phosphorylation of glucose analogs via the phosphoenolpyruvate: mannose-phosphotransferase system in Streptococcus lactis.

The bacterial phosphoenolpyruvate:sugar-phosphotransferase system (PTS) mediates the vectorial translocation and concomitant phosphorylation of sugars. The question arises of whether the PTS can also mediate the phosphorylation of intracellular sugars. To investigate this possibility in Streptococcus lactis 133, lactose derivatives have been prepared containing 14C-labeled 2-deoxy-glucose (2DG), 2-deoxy-2-fluoro-D-glucose (2FG), or alpha-methylglucoside as the aglycon substituent of the disaccharide. Two of the compounds, beta-O-D-galactopyranosyl-(1,4')-2'-deoxy-D-glucopyranose (2'D-lactose) and beta-O-D-galactopyranosyl-(1,4')-2'-deoxy-2'-fluoro-D-glucopyranose (2'F-lactose), were high-affinity substrates of the lactose-PTS. After translocation, the radiolabeled 2'F-lactose 6-phosphate (2'F-lactose-6P) and 2'D-lactose-6P derivatives were hydrolyzed by P-beta-galactoside-galactohydrolase to galactose-6P and either [14C]2FG or [14C]2DG, respectively. Thereafter, the glucose analogs appeared in the medium, but the rates of sugar exit from mannose-PTS-defective mutants were greater than those determined in the parent strain. Unexpectedly, the results of kinetic studies and quantitative analyses of intracellular products in S. lactis 133 showed that initially (and before exit) the glucose analogs existed primarily in phosphorylated form. Furthermore, the production of intracellular [14C]2FG-6P and [14C]2DG-6P (during uptake of the lactose analogs) continued when the possibility for reentry of [14C]2FG and 2DG was precluded by addition of mannose-PTS inhibitors (N-acetylglucosamine or N-acetylmannosamine) to the medium. By contrast, (i) only [14C]2DG, [14C]2FG, and trace amounts of [14C]2FG-6P were found in cells of a mannose-PTS-defective mutant, and (ii) only [14C]2FG and [14C]2DG were present in cells of a double mutant lacking both mannose-PTS and glucokinase activities. We conclude from these data that the mannose-PTS can effect the intracellular phosphorylation of glucose and its analogs in S. lactis 133.

Biological Transport↗
PubMedDate not supplied

[Effect of KH2PO4 on Streptococcus lactis growth and nisin synthesis when the medium is kept at a constant pH].

When the pH of the medium was maintained at the level of 6.6--6.8 and the content of KH2PO4 in it was decreased, the biosynthetic activity of Streptococcus lactis, strain MGU, became lower. The culture assimilated low quantities of phosphorus from KH2PO4 at a high concentration of this salt in the medium; presumably, the culture required large quantities of potassium ions. If the pH of the medium is maintained at a constant value, the fermentation can be stopped 21 hr after the beginning of cultivation of Str. lactis, strain MGU.

Hydrogen-Ion Concentration↗
PubMed1983

Plasmid linkage of the D-tagatose 6-phosphate pathway in Streptococcus lactis: effect on lactose and galactose metabolism.

The three enzymes of the D-tagatose 6-phosphate pathway (galactose 6-phosphate isomerase, D-tagatose 6-phosphate kinase, and tagatose 1,6-diphosphate aldolase) were absent in lactose-negative (Lac-) derivatives of Streptococcus lactis C10, H1, and 133 grown on galactose. The lactose phosphoenolpyruvate-dependent phosphotransferase system and phospho-beta-galactosidase activities were also absent in Lac- derivatives of strains H1 and 133 and were low (possibly absent) in C10 Lac-. In all three Lac- derivatives, low galactose phosphotransferase system activity was found. On galactose, Lac- derivatives grew more slowly (presumably using the Leloir pathway) than the wild-type strains and accumulated high intracellular concentrations of galactose 6-phosphate (up to 49 mM); no intracellular tagatose 1,6-diphosphate was detected. The data suggest that the Lac phenotype is plasmid linked in the three strains studied, with the evidence being more substantial for strain H1. A Lac- derivative of H1 contained a single plasmid (33 megadaltons) which was absent from the Lac- mutant. We suggest that the genes linked to the lactose plasmid in S. lactis are more numerous than previously envisaged, coding for all of the enzymes involved in lactose metabolism from initial transport to the formation of triose phosphates via the D-tagatose 6-phosphate pathway.

Aldehyde-Lyases↗
PubMedDate not supplied

[Fragmentation of the lactose-protease plasmid in lactose-negative derivatives of Streptococcus lactis and S. lactis ssp. diacetylactis].

DNA analysis showed the presence of plasmids in all 29 strains of mesophilic lactic streptococci. Their number ranged from 1 to 9 and their molecular weight extended from 1.8 to 45 megadaltons (Md). Comparison of the plasmid profiles from 9 strains of Streptococcus lactis, 3 strains of S. lactis ssp. diacetylactis and from their Lac-,Prt-variants was carried out. In most of the strains, a single plasmid of 27 to 45 Md carried both the lactose and protease (lac and prt) determinants. In Lac- variants, this composite plasmid may at times be lost; in most derivatives, this plasmid was fragmented into several smaller plasmids. Fragmentation resulted in the inactivation of lac genes and often of prt genes; sometimes prt genes remained intact in one of these new plasmids. Fragmentation of the plasmid may also take place without inactivation of these metabolic genes. Restriction analysis of the lactose-protease plasmid from 3 strains of S. lactis and from one Lac-variant confirmed the plasmid fragmentation phenomenon, and led to a proposal for physical mapping of the plasmid and preliminary localization of the lac-prt genes.

DNA Restriction Enzymes↗
PubMed1981

Carbohydrate Fermentation by Streptococcus cremoris and Streptococcus lactis Growing in Agar Gels.

When lactic streptococci were embedded in agar gels and incubated at 30 degrees C, the end products of carbohydrate fermentation depended on the initial cell density, which determined the subsequent distribution and size of colonies in the gel. With high initial cell densities, microcolonies formed close together and lactose and glucose were converted almost entirely to lactate. However, inoculation with a small number of cells, which then grew to form widely spaced and comparatively large colonies, resulted in up to 30% diversion of end product, usually to formate, ethanol, and acetate. In these "low-colony-density" gel cultures, the initial rate of fermentation was exponential and only lactate was formed. However, this rate then became linear and fermentation became progressively more heterolactic. Streptococcus lactis ML(8) was the only strain among the 10 tested which remained homolactic. Incubation at temperatures either above or below the optimum for growth and metabolism decreased the diversion to end products other than lactate. The change from homo- to heterolactic fermentation appears to be caused by carbohydrate depletion in the vicinity of the colony, so that fermentation is then limited by the diffusion of substrate. Growth of cells on gel surfaces exposed to air resulted in up to 40% diversion of end product from lactate, mainly to CO(2), acetoin, 2,3-butanediol, and acetate. Six of the 12 Streptococcus cremoris strains tested remained homolactic under these aerobic conditions, whereas all 8 of the S. lactis strains tested, including ML(8), were heterolactic.

Journal Article↗
PubMed1987

Selection of Streptococcus lactis Mutants Defective in Malolactic Fermentation.

An enrichment medium and a new sensitive medium were developed to detect malolactic variants in different strains of lactic bacteria. Factors such as the concentration of glucose and l-malate, pH level, and the type of indicator dye used are discussed with regard to the kinetics of malic acid conversion to lactic acid. Use of these media allowed a rapid and easier screening of mutagenized streptococcal cells unable to ferment l-malate. A collection of malolactic-negative mutants of Streptococcus lactis induced by UV, nitrosoguanidine, or transposonal mutagenesis were characterized. The results showed that several mutants were apparently defective in the structural gene of malolactic enzyme, whereas others contained mutations which may either inactivate a putative permease or affect a regulatory sequence.

Journal Article↗
PubMed1978

Stabilization of Lactose Metabolism in Streptococcus lactis C2.

The integration of the lactose plasmid from lactic streptococci into the host chromosome could stabilize this trait for dairy fermentations. Sixty lactose-positive (Lac) transductants of lactose- and proteinase-negative (Lac Prt) LM0220 were induced for temperature phage by UV irradiation or mitomycin C. Four of the transductants, designated KB18, KB21, KB54, and KB58, yielded lysates demonstrating less than one Lac transductant per 0.2 ml of phage lysate. Successive transferring in the presence of acriflavine did not yield Lac segregants from KB18, KB21, KB54, or KB58, whereas Streptococcus lactis C2 (parent culture) and three other Lac transductants showed 12 to 88% conversion from Lac to Lac within 6 to 10 repetitive transfers. When grown in continuous culture, KB21 did not show any Lac variants in 168 h, while S. lactis C2 had 96% conversion from Lac to Lac in 144 h. Agarose gel electrophoresis of plasmid DNA isolated from KB18, KB21, KB54, and KB58 revealed that the lactose plasmid, pLM2103, normally present in Lac transductants, was missing. This suggested integration of the transferred lactose plasmid into the chromosome. In contrast to phage lysates induced from S. lactis C2, which exhibited an exponential decrease in the number of Lac transductants after exposure to small doses of UV irradiation, the transduction frequency for lactose metabolism was stimulated by UV irradiation of lysates from KB58. The latter indicated chromosomal linkage for lac and that integration of the lactose genes plasmid into the chromosome had occurred.

Journal Article↗
PubMed1979

Change from homo- to heterolactic fermentation by Streptococcus lactis resulting from glucose limitation in anaerobic chemostat cultures.

Lactic streptococci, classically regarded as homolactic fermenters of glucose and lactose, became heterolactic when grown with limiting carbohydrate concentrations in a chemostat. At high dilution rates (D) with excess glucose present, about 95% of the fermented sugar was converted to l-lactate. However, as D was lowered and glucose became limiting, five of the six strains tested changed to a heterolactic fermentation such that at D = 0.1 h(-1) as little as 1% of the glucose was converted to l-lactate. The products formed after this phenotypic change in fermentation pattern were formate, acetate, and ethanol. The level of lactate dehydrogenase, which is dependent upon ketohexose diphosphate for activity, decreased as fermentation became heterolactic with Streptococcus lactis ML(3). Transfer of heterolactic cells from the chemostat to buffer containing glucose resulted in the nongrowing cells converting nearly 80% of the glucose to l-lactate, indicating that fine control of enzyme activity is an important factor in the fermentation change. These nongrowing cells metabolizing glucose had elevated (ca. twofold) intracellular fructose 1,6-diphosphate concentrations ([FDP](in)) compared with those in the glucose-limited heterolactic cells in the chemostat. [FDP](in) was monitored during the change in fermentation pattern observed in the chemostat when glucose became limiting. Cells converting 95 and 1% of the glucose to l-lactate contained 25 and 10 mM [FDP](in), respectively. It is suggested that factors involved in the change to heterolactic fermentation include both [FDP](in) and the level of lactate dehydrogenase.

Acetates↗