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PubMed1993

Effect of humidity on solid-state isomerization of various kinds of lactose during grinding.

The effect of humidity on isomerization during grinding of alpha-monohydrate, alpha-anhydrate and beta-anhydrate of lactose was investigated. Samples were ground in an agate centrifugal ball mill at 270 rev min-1 at room temperature (21 degrees C) and at 5 and 60% relative humidity. Crystallinity of the ground lactose was measured by Hermans' method from the powder X-ray diffraction profiles. The alpha- and beta-lactose content of the ground lactose was measured by using angular rotation spectrophotometry. The crystalline lactose samples were transformed into noncrystalline solids by mechanical stress during grinding. After grinding, the adsorbed water content of all ground lactose samples increased, and the isomerized amount increased with increase of the water content during grinding at 5 and 60% relative humidity. The results suggest that the isomerization rate of alpha-monohydrate during grinding may depend on the crystallinity, but those of alpha- and beta-anhydrate depend on the content of adsorbed water.

Crystallization↗

PubMed2007

Analysis of the mechanism and regulation of lactose transport and metabolism in Clostridium acetobutylicum ATCC 824.

Although the acetone-butanol-ethanol fermentation of Clostridium acetobutylicum is currently uneconomic, the ability of the bacterium to metabolize a wide range of carbohydrates offers the potential for revival based on the use of cheap, low-grade substrates. We have investigated the uptake and metabolism of lactose, the major sugar in industrial whey waste, by C. acetobutylicum ATCC 824. Lactose is taken up via a phosphoenolpyruvate-dependent phosphotransferase system (PTS) comprising both soluble and membrane-associated components, and the resulting phosphorylated derivative is hydrolyzed by a phospho-beta-galactosidase. These activities are induced during growth on lactose but are absent in glucose-grown cells. Analysis of the C. acetobutylicum genome sequence identified a gene system, lacRFEG, encoding a transcriptional regulator of the DeoR family, IIA and IICB components of a lactose PTS, and phospho-beta-galactosidase. During growth in medium containing both glucose and lactose, C. acetobutylicum exhibited a classical diauxic growth, and the lac operon was not expressed until glucose was exhausted from the medium. The presence upstream of lacR of a potential catabolite responsive element (cre) encompassing the transcriptional start site is indicative of the mechanism of carbon catabolite repression characteristic of low-GC gram-positive bacteria. A pathway for the uptake and metabolism of lactose by this industrially important organism is proposed.

Amino Acid Sequence↗

PubMed1978

Lactose variability of Escherichia coli in thermally stressed reactor effluent waters.

Lactose-utilizing and nalidixic acid-resistant populations of Escherichia coli, having an optimum growth temperature of 37 degrees C, were placed in modified diffusion chambers. The chambers were submerged in the epilimnion and hypolimnion of a 1,100-hectare lake (Par Pond) which receives cooling water from a nuclear production reactor. Control chambers were placed in a deep-water reservoir and a Flowing-Streams Laboratory, both of which had comparable temperatures to Par Pond. The populations of E. coli were sampled regularly for up to 3 weeks. Viability of the bacteria was determined by dilution plating to nutrient agar followed by replicate plating onto selective medium to determine lactose utilization and nalidixic acid sensitivity. Initial populations of E. coli were lactose positive but changed to lactose negative in Par Pond when the reactor was operating (i.e., cooling water from the heat exchangers was being discharged to the lake). This alteration occurred most rapidly in the chambers closest to the cooling-water discharge point. Such changes did not occur in a deep-water reservoir, in Par Pond when the reactor was not operating, or in the Flowing-Streams Laboratory. The nalidixic acid-resistant characteristic remained stable regardless of the chambers' placement or reactor operations. Although the reasons for such alterations are unclear, it appears that lactose-negative populations of E. coli are selected for in these reactor effluent waters. The loss of the lactose characteristic prevents the recognition and identification of E. coli in this cooling lake (when the reactor is operating) and may prevent the assessment of water quality based on coliform recognition.

Drug Resistance, Microbial↗

PubMed1983

Distribution of Vibrio vulnificus and other lactose-fermenting vibrios in the marine environment.

During the summer of 1981, 3,887 sucrose-negative vibrios were isolated from seawater, sediment, plankton, and animal samples taken from 80 sites from Miami, Fla., to Portland, Maine. Of these, 4.2% were able to ferment lactose. The lactose-positive strains isolated from the various samples correlated positively with pH and turbidity of the water, vibrios in the sediment and oysters, and total bacterial counts in oysters. Negative correlations were obtained for water salinity. Numerical taxonomy was performed on 95 of the lactose-fermenting environmental isolates and 23 reference strains. Five clusters resulted, with the major cluster containing 33 of the environmental isolates and all of the Vibrio vulnificus reference strains. The 33 isolates, which produced an acid reaction in lactose broth within hours of initial inoculation, represented 20% of all lactose-fermenting vibrios studied. These isolates were nearly identical phenotypically to clinical strains of V. vulnificus studied by the Centers for Disease Control, Atlanta, Ga., and by our laboratory, and their identification was confirmed by DNA-DNA hybridization studies. V. vulnificus was isolated from all sample types and from Miami to Cape Cod, Mass., and comparison of the environmental parameters of the eight subsites yielding this species with those of all 80 subsites revealed no significant differences. The majority of the isolates were obtained from animals, with clams providing most (84%) of these. On injection into mice, 82% of the V. vulnificus isolates resulted in death. Members of the remaining four clusters contained strains which differed from V. vulnificus in such phenotypic traits as luminescence and in urease or H(2)S production. None of the other reference cultures, including nine other Vibrio species, were contained in the remaining clusters, and these isolates could not be identified. Most of these were also lethal for mice. Phenotypic differences, potential pathogenicity, and geographic distribution of the five clusters were examined. It is concluded that V. vulnificus is a ubiquitous organism, both geographically and in a variety of environmental sources, although it occurs in relatively low numbers. The public health significance of this organism and of the other unidentified lactose-fermenting Vibrio species is discussed.

Fermentation↗

PubMed1993

Fermentation of lactose by yeast cells secreting recombinant fungal lactase.

Strains of Saccharomyces cerevisiae transformed with a yeast multicopy expression vector carrying the cDNA for Aspergillus niger secretory beta-galactosidase under the control of ADH1 promoter and terminator were studied for their fermentation properties on lactose (V. Kumar, S. Ramakrishnan, T. T. Teeri, J. K. C. Knowles, and B. S. Hartley, Biotechnology 10:82-85, 1992). Lactose was hydrolyzed extracellularly into glucose and galactose, and both sugars were utilized simultaneously. Diauxic growth patterns were not observed. However, a typical biphasic growth was observed on a mixture of glucose and galactose under aerobic and anaerobic conditions with transformants of a haploid S. cerevisiae strain, GRF167. Polyploid distiller's yeast (Mauri) transformants were selected simply on the basis of the cloned gene expression on X-Gal (5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside) plates. Rapid and complete lactose hydrolysis and higher ethanol (0.31 g/g of sugar) and biomass (0.24 g/g of sugar) production were observed with distiller's yeast grown under aerobic conditions. A constant proportion (10%) of the population retained the plasmid throughout the fermentation period (48 h). Nearly theoretical yields of ethanol were obtained under anaerobic conditions on lactose, glucose, galactose, and whey permeate media. However, the rate and the amount of lactose hydrolysis were lower under anaerobic than aerobic conditions. All lactose-grown cells expressed partial galactokinase activity.

Aerobiosis↗

PubMed1984

Role of the phosphoenolpyruvate-dependent glucose phosphotransferase system of Streptococcus mutans GS5 in the regulation of lactose uptake.

When Streptococcus mutans GS5 was grown in equimolar (5 mM) amounts of glucose and lactose, a classical diauxic growth curve was obtained. Glucose was taken up during the first growth phase, followed by a 60-min lag, and then lactose was transported. Synthesis of lactose phosphotransferase system (PTS) enzymes was repressed until the complete exhaustion of glucose, indicative of an inducer exclusion mechanism of repression. The enzyme phospho-beta-galactosidase, however, was found in small amounts even in the presence of glucose. Repression was not observed when GS5 was grown in equimolar amounts of fructose and lactose. Although fructose was taken up preferentially, synthesis of the lactose PTS occurred from the onset of growth in these sugars. It is proposed that a component of the glucose PTS may be a regulatory factor in lactose transport. Glucose PTS- mutants did not display diauxic growth in glucoselactose mixtures and, in fact, transported the disaccharide preferentially.

Fructose↗

PubMed1970

Mechanisms of lactose utilization by lactic acid streptococci: enzymatic and genetic analyses.

The apparent instability of beta-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-beta-d-galactoside-6-phosphate (ONPG-6-P), indicating the presence of a different enzyme. In addition, lactose metabolism in S. lactis C(2)F was found to involve enzyme I (EI), 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 C(2)F, defective in lactose metabolism, possessed the phenotype lac(-) gal(-). These strains were unable to accumulate (14)C-thiomethyl-beta-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 beta-galactosidase, could be separated into several classes, which indicated that this organism is not dependent upon the PEP-phosphotransferase system for lactose metabolism.

Carbon Isotopes↗

PubMed1976

lacY mutant of Escherichia coli with altered physiology of lactose induction.

A mutant of Escherichia coli is described that grew on lactose only in the presence of isopropylthiogalactoside. This cell contained a defect in the lacY gene that resulted in the formation of a transport system with a poor affinity for lactose. The inability to grow on lactose alone was due to the failure of induction by this disaccharide. This failure of inducation was presumably due to a defect in lactose accumulation which resulted in significant reduction in the formation of allo-lactose, the true inducer of lac operon. These results are consistent with the view that the capacity to accumulate lactose plays an important physiological role in the induction of the enzymes necessary for its utilization.

Biological Transport, Active↗

PubMed1977

Inorganic salts resistance associated with a lactose-fermenting plasmid in Streptococcus lactis.

Present evidence indicates that lactose metabolism in group N streptococci is linked to plasmid deoxyribonucleic acid. Lactose-positive (Lac+) Streptococcus lactis and lactose-negative (Lac-) derivatives were examined for their resistance to various inorganic ions. Lac+ S. lactis strains ML3, M18, and C2 were found more resistant to arsenate (7.5- to 60.2-fold), arsenite (2.25- to 3.0-fold), and chromate (6.6- to 9.4-fold), but more sensitive to copper (10.0- to 13.3-fold) than their Lac- derivatives. These results suggested that genetic information for resistance and/or sensitivity to these ions resides on the "lactose plasmid." Kinetics of ultraviolet irradiation inactivation of transducing ability for lactose metabolism and arsenate resistance confirmed the plasmid location of the two markers. Lac+ transductants from S. lactis C2 received genetic determinants for resistance to arsenate, arsenite, and chromate but not for copper sensitivity. In this case, resistance markers were lost when the transductants became Lac- but the derivatives remained copper resistant. The resistant markers for arsenate and arsenite could not be identified as separate genetic loci, but chromate resistance and copper sensitivity markers were found to be independent genetic loci. The "lactose plasmid" from S. lactis C10 possessed the genetic loci for arsenate and arsenite resistance but not for chromate resistance or copper sensitivity.

Arsenates↗

PubMed1979

Lactose metabolism involving phospho-beta-galactosidase in Klebsiella.

Klebsiella strain RE1755A is a Lac- Gal- mutant which has lost both of its lac operons, but possesses a gene specifying beta-galactosidase III, an enzyme which hydrolyzes o-nitrophenyl-beta-D-galactopyranoside but does not hydrolyze lactose. Selective pressure was applied to isolate mutants able to utilize lactose. The lactose-utilizing mutants obtained were shown to possess an unaltered beta-galactosidase III. Lactose utilization was shown to result from a pleiotropic mutation which also (i) permits galactose utilization and (ii) prevents induction of beta-galactosidase III synthesis by lactose. Evidence is presented suggesting that a phospho-beta-galactosidase enzyme is involved in lactose metabolism.

Galactosephosphates↗

PubMed1990

Reconstitution of an active lactose carrier in vivo by simultaneous synthesis of two complementary protein fragments.

Escherichia coli lactose permease mediates the proton-driven translocation of galactosides across the cytoplasmic membrane. To define regions important for membrane insertion as well as for biological function, we constructed plasmids encoding different portions of the lactose carrier. Among several lacY deletions, two were obtained that encoded mutant proteins with complementary amino acid sequences. The truncated polypeptide Y71/1 (amino acid residues 1 to 71) comprises the first two alpha-helices predicted for the intact protein, and polypeptide delta Y4-69 carries an internal deletion of this region. Regulated coexpression of these lacY-DNA segments governed by separate but identical lacOP control regions resulted in functional complementation with the following characteristics. (i) Simultaneous synthesis of both incomplete proteins restored transport activity in transport-negative cells, measured as accumulation of [14C]lactose. (ii) Under complementing conditions, but not in the absence of the smaller N-terminal protein, specific radiolabeling of the larger polypeptide by N-ethylmaleimide was prevented by substrate. (iii) The presence of the complementing N-terminal polypeptide was also required for the detection of the larger C-terminal protein by antibodies directed against the C terminus of lactose permease, indicating a stabilizing effect contributed by the smaller N-terminal fragment. Thus, coexpression of lacY mutant genes encoding two nonoverlapping portions of the lactose carrier resulted in reconstitution of a two-subunit protein in the cytoplasmic membrane exhibiting biological properties of intact lactose permease.

Biological Transport, Active↗

PubMed1992

Nucleotide and deduced amino acid sequences of the lacR, lacABCD, and lacFE genes encoding the repressor, tagatose 6-phosphate gene cluster, and sugar-specific phosphotransferase system components of the lactose operon of Streptococcus mutans.

The complete nucleotide sequences of lacRABCDF and partial nucleotide sequence of lacE from the lactose operon of Streptococcus mutans are presented. Comparison of the streptococcal lac determinants with those of Staphylococcus aureus and Lactococcus lactis indicate exceptional protein and nucleotide identity. The deduced polypeptides also demonstrate significant, but lower, sequence similarity with the corresponding lactose proteins of Lactobacillus casei. Additionally, LacR has sequence homology with the repressor (DeoR) of the Escherichia coli deoxyribonucleotide operon, while LacC is similar to phosphokinases (FruK and PfkB) from E. coli. The primary translation products of the lacRABCDFE genes are polypeptides of 251 (M(r) 28,713), 142 (M(r) 15,610), 171 (M(r) 18,950), 310 (M(r) 33,368), 325 (M(r) 36,495), 104 (M(r) 11,401), and 123 (NH2-terminal) amino acids, respectively. As inferred from their direct homology to the staphylococcal lac genes, these determinants would encode the repressor of the streptococcal lactose operon (LacR), galactose-6-phosphate isomerase (LacA and LacB), tagatose-6-phosphate kinase (LacC), tagatose-1,6-bisphosphate aldolase (LacD), and the sugar-specific components enzyme III-lactose (LacF) and enzyme II-lactose (LacE) of the S. mutans phosphoenolpyruvate-dependent phosphotransferase system. The nucleotide sequence encompassing the S. mutans lac promoter appears to contain repeat elements analogous to those of S. aureus, suggesting that repression and catabolite repression of the lactose operons may be similar in these organisms.

Amino Acid Sequence↗

PubMed1983

Lactose-fermenting, multiple drug-resistant Salmonella typhi strains isolated from a patient with postoperative typhoid fever.

Two lactose-fermenting Salmonella typhi strains were isolated from bile and blood specimens of a typhoid fever patient who underwent a cholecystectomy due to cholelithiasis. One lactose-fermenting S. typhi strain was also isolated from a pus specimen which was obtained at the tip of the T-shaped tube withdrawn from the operative wound of the common bile duct of the patient. These three lactose-fermenting isolates: GIFU 11924 from bile, GIFU 11926 from pus, and GIFU 11927 from blood, were phenotypically identical to the type strain (GIFU 11801 = ATCC 19430 = NCTC 8385) of S. typhi, except that the three strains fermented lactose and failed to blacken the butt of Kligler iron agar or triple sugar iron agar medium. All three lactose-fermenting strains were resistant to chloramphenicol, ampicillin, sulfomethoxazole, trimethoprim, gentamicin, cephaloridine, and four other antimicrobial agents. The type strain was uniformly susceptible to these 10 drugs. The strain GIFU 11925, a lactose-negative dissociant from strain GIFU 11926, was also susceptible to these drugs, with the sole exception of chloramphenicol (minimal inhibitory concentration, 100 micrograms/ml).

Anti-Bacterial Agents↗

PubMed1984

Escherichia coli growth on lactose requires cycling of beta-galactosidase products into the medium.

Growth on lactose was found to be restricted in an Escherichia coli strain deficient in its ability to transport glucose and galactose. If the latter sugars were removed from the medium as they were being produced, a wild-type strain grew only poorly, while the transport-deficient strain did not grow at all. These results suggested that all of the products of beta-galactosidase action on lactose are released into the medium before being metabolized. This contention was strongly supported by the finding that the appearance of products in the medium was equal to lactose disappearance at three limiting lactose concentrations and by an experiment which showed that essentially all of the label from added lactose ( [1-14C]glucose) was found in the medium as glucose when chased with unlabelled lactose.

Culture Media↗

PubMed1989

Cyclic nucleotides and polyamines in prolactin stimulation of lactose biosynthesis.

The possible roles of adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) and of polyamines on the early effect of prolactin (PRL) on lactose biosynthesis have been investigated in cultured mammary gland explants derived from mice 12-14 days pregnant. Elevated cAMP concentrations impaired the PRL stimulation of [3H]glucose incorporation into lactose. Adding dibutyryl cAMP (0.1-0.5 mM) or phosphodiesterase inhibitors [methyl isobutylxanthine (0.1-0.5 mM) or theophylline (0.5-5.0 mM)] to the culture medium abolished the PRL response. The addition of 8-bromo cGMP (0.5 mM) with or without 1.0 mM spermidine had no effect on the PRL stimulation of lactose synthesis. By itself, 1.0 mM spermidine consistently produces a small but significant PRL-like stimulation of lactose synthesis in this system. Ongoing polyamine metabolism appears to be necessary for the PRL effect on lactose synthesis because 100 microM methylglyoxal bis(guanyl hydrazone), an inhibitor of S-adenosyl methionine decarboxylase, abolished the PRL response. alpha-Difluoromethylornithine, an inhibitor of ornithine decarboxylase activity, at concentrations from 1.0 to 10 mM had no effect on the PRL stimulation of lactose synthesis.

Animals↗

PubMed2006

Hydrogen breath test for diagnosis of lactose malabsorption: the importance of timing and the number of breath samples.

BACKGROUND: The hydrogen breath test (H(2)BT) is the most widely used procedure in the diagnostic workup of lactose malabsorption and lactose intolerance. AIM: To establish whether a simplified two- or three-sample test may reduce time, costs and staff resources without reducing the sensitivity of the procedure. PATIENTS AND METHODS: Data from 1,112 patients (292 men, 820 women) with a positive 4 h, nine-sample H(2)BT were retrospectively analyzed. Patients were stratified according to the degree of lactose malabsorption, the occurrence and type of symptoms. Loss of sensitivity in the procedure was evaluated taking into account two-sample tests (0 min and 120 min or 0 min and 210 min) or three-sample tests (0 min, 120 min and 180 min or 0 min, 120 min and 210 min). RESULTS: Using a two-sample test (0 min and 120 min or 0 min and 210 min) the false-negative rate was 33.4% and 22.7%, respectively. With a three-sample test (0 min, 120 min and 180 min or 0 min, 120 min or 210 min), lactose malabsorption was diagnosed in 91.2% (1,014 of 1,112) patients and in 96.1% (1,068 of 1,112) patients, respectively. Of 594 patients with abdominal symptoms, 158 (26.6%) and 73 (12.2%) would have false-negative results with 0 min and 120 min or 0 min and 210 min two-sample tests, respectively. The three-sample tests, 0 min, 120 min and 180 min or 0 min, 120 min and 210 min, have a false-negative rate of 5.9% and 2.1%, respectively. CONCLUSIONS: A three-sample H(2)BT is time- and cost-sparing without significant loss of sensitivity for the diagnosis both of lactose malabsorption and lactose intolerance.

Adult↗

PubMed1987

Effect of dietary and infused lactose on rat intestinal lymph lipids.

Twenty-four male, 6- to 8-week-old Sprague-Dawley rats were fed one of two skim-milk-based diets or stock laboratory diet for 100-120 days to assess the effect of dietary and infused lactose on intestinal lymph lipids. One skim-milk-based diet had its lactose enzymatically hydrolyzed by commercial beta-galactosidase to its constituent monosaccharides galactose and glucose, while the second skim milk diet was unaltered. Serum triglycerides, but not serum cholesterol, were higher in the lactose- versus the glucose-/galactose-adapted rats at 90 days. There was no diet-associated qualitative difference in serum lipoproteins as analyzed by agarose gel electrophoresis. After the rats had consumed the diets for 100-120 days, 0.9% saline and 20% solutions of lactose, and equimolar mixtures of glucose/galactose, glucose and maltose were infused sequentially via a duodenal cannula, then intestinal lymph was collected via a mesenteric lymph duct cannula, the only significant difference was a 134% increase in lymph cholesterol, but not lymph triglyceride output, when lactose was infused into lactose-adapted rats.

Adaptation, Physiological↗

PubMed1999

Synthesis of polystyrene nanospheres having lactose-conjugated hydrophilic polymers on their surfaces and carbohydrate recognition by proteins.

We prepared a poly(vinylamine)-grafted polystyrene nanosphere by the free radical polymerization of poly(N-vinylacetamide) macromonomer and styrene with AIBN in ethanol and subsequent acid hydrolysis. We conjugated lactose on the nanosphere by an amide linkage and found that the lactose was recognized by a galactose-specific lectin RCA120, which was analyzed by enzyme-linked lectin assay (ELLA). The binding ability of the lectin to lactose on the nanosphere was at least 10(2) times larger than that to a monomeric lactose. Binding ability was clearly affected by the lactose density on the nanosphere and showed a maximum value at the suitable surface density of lactose. We found that the carbohydrate-conjugated nanosphere would be a useful biomaterial for a site specific drug carrier.

Carbohydrate Metabolism↗