Effect of Temperature on Heterotrophic Glucose Uptake, Mineralization, and Turnover Rates in Lake Sediments

The V_max and turnover rates (TR) of [U-¹⁴C]glucose uptake and mineralization of Lake Kinneret (Israel) sediment are temperature dependent. The following activation energies were determined: glucose uptake, ~15,000 cal (62,760 J); TR of glucose uptake, ~10,000 cal (41,840 J); glucose mineralization, 7,500 to 15,000 cal (31,380 to 62,760 J); and TR of glucose mineralization, ~15,000 cal. Q₁₀ values varied as follows: glucose uptake, ~2.3; TR of glucose uptake, ~1.8; and glucose mineralization, ~2.5. K + S_n values increased slightly with temperature and might reflect an increased K with increased temperatures. Glucose respiration/uptake ratios were low (9.5 to 12%) and were apparently not greatly influenced by the presence or absence of oxygen or by different assay temperatures. Aerobic or anaerobic sediments assayed under either aerobic or anaerobic conditions did not exhibit greatly different V_max, TR, or K + S_n values.     

Stability of the Plasma Membrane in Saccharomyces rouxii and Its Relationship to Glucose Tolerance

The stability of spheroplasts from the osmotrophic yeast Saccharomyces rouxii was studied in buffered solutions of mannitol and glucose. The plasma membranes from cells grown in high glucose concentrations were more stable to osmotic lysis than were membranes from cells grown in lower glucose concentrations. Mannitol was a better osmotic stabilizer than glucose, except when the cells were grown in a high glucose concentration. Spheroplasts from a glucose tolerant-deficient mutant were much less stable than the corresponding spheroplasts from the parent strain, especially when suspended in glucose solutions. These results suggest an involvement of the plasma membrane in the glucose-tolerant mechanism of S. rouxii.     

Commensalistic Interaction Between Lactobacillus acidophilus and Propionibacterium shermanii

Propionibacterium shermanii and Lactobacillus acidophilus were grown in batch mixed culture in a 5-liter fermenter under controlled conditions of pH 5.8 and 35°C on a semisynthetic medium with glucose as an energy source. Cellular efficiencies and fermentation balances were developed for this pair and compared with P. shermanii grown in pure culture on glucose, lactate, and a mixture of these substrates and with L. acidophilus grown on glucose. P. shermanii had ATP yield coefficient values of 17 for each substrate alone but had an average value of 30 for substrate mixtures. Growth rates were similar for P. shermanii on glucose or lactate but higher cell yields were observed for glucose. P. shermanii used both lactate and glucose in mixed substrate until lactate was exhausted, and growth rates slowed thereafter. L. acidophilus had a similar ATP yield coefficient of 15 but produced lower cell yields than did P. shermanii on glucose. Mixed culture of both microorganisms on glucose resulted in much faster and nearly equal growth rates for both and no lactate accumulation in the medium. Acetic acid production rates per generation were lower in mixed culture, suggesting use by the growing culture. The cause of the synergistic effect was not determined but may be due to the rapid production and removal of lactate or CO₂ enhancement in mixed culture.     

Self Blood Glucose Monitoring Underestimates Hyperglycemia And Hypoglycemia As Compared To Continuous Glucose Monitoring In Type 1 And Type 2 Diabetes

Objective: When glucose records from self blood glucose monitoring (SBGM) do not reflect estimated average glucose from glycosylated hemoglobin (HgBA1) or when patients' clinical symptoms are not explained by their SBGM records, clinical management of diabetes becomes a challenge. Our objective was to determine the magnitude of differences in glucose values reported by SBGM versus those documented by continuous glucose monitoring (CGM).Methods: The CGM was conducted by a clinical diabetes educator (CDE)/registered nurse by the clinic protocol, using the Medtronic iPRO2™ system. Patients continued SBGM and managed their diabetes without any change. Data from 4 full days were obtained, and relevant clinical information was recorded. De-identified data sets were provided to the investigators.Results: Data from 61 patients, 27 with type 1 diabetes (T1DM) and 34 with T2DM were analyzed. The lowest, highest, and average glucose recorded by SBGM were compared to the corresponding values from CGM. The lowest glucose values reported by SBGM were approximately 25 mg/dL higher in both T1DM (P = .0232) and T2DM (P = .0003). The highest glucose values by SBGM were approximately 30 mg/dL lower in T1DM (P = .0005) and 55 mg/dL lower in T2DM (P<.0001). HgBA1c correlated with the highest and average glucose by SBGM and CGM. The lowest glucose values were seen most frequently during sleep and before breakfast; the highest were seen during the evening and postprandially.Conclusion: SBGM accurately estimates the average glucose but underestimates glucose excursions. CGM uncovers glucose patterns that common SBGM patterns cannot.Abbreviations: CDE = certified diabetes educator; CGM = continuous glucose monitoring; HgBA1c = glycosylated hemoglobin; MAD = mean absolute difference; SBGM = self blood glucose monitoring; T1DM = type 1 diabetes; T2DM = type 2 diabetes     

On-line control of glucose concentration using an automatic glucose analyzer

The fundamental characteristics of an automatic glucose analyzer which consists of sampling, sensor, and operation units were examined. The glucose sensor is a dual cathode type which has an immobilized glucose oxidase membrane coupled with an oxygen sensor. Using this glucose sensor combined with an automatic sampling device, on-off control of the glucose concentration in fed-batch cultures of Saccharomyces cerevisiae was carried out. When the glucose concentration to be controlled was set at 0.3 and 10 g/l, the concentration was well maintained within the range of 0.08−0.54 g/l in the former, and within 9.2–11.1 g/l in the latter. In the former experiment, 1.67 g/l of ethanol was produced at the end of cultivation (OD₅₇₀=34). On the other hand, 12.9 g/l of ethanol was accumulated at the end of cultivation (OD₅₇₀=43) in the latter experiment. Fed-batch cultures of Micrococcus ruteus were also carried out. The glucose concentration was set at 2.5 g/l. The microorganism grew up to OD₆₁₀=264 and the glucose concentration was maintained within 2.0 and 3.1 g/l.     

Fasciola hepatica: Energy sources and metabolism

Gas chromatographic determination of biliary glucose in the rat showed only low levels were present. Although flukes took up glucose from the bile in vivo, biliary glucose could not be a major energy source as occurs in Hédon Fleig solution in vitro. Alanine, arginine, glutamate, histidine, phenylalanine, and serine were not metabolised in vitro to volatile fatty acids, and mixtures of peptides or amino acids failed to spare glycogen breakdown in the absence of glucose. Although glycerol was metabolised in vitro, the main energy source of the fluke in vivo has not been identified. Labelling studies confirmed that glucose taken up in vitro is degraded via glycolysis rather than the pentose phosphate pathway.     

Modified glucose-oxidase/peroxidase residual glucose assay for use with anaerobic bacteria

Because Lactobacillus species compounds that interfere with the o-toluidine assay for glucose, use of the glucose-oxidase/peroxidase method was investigated. Although this method gave satisfactory results for Lactobacillus acidophilus, L. plantarum and L. lactis cultured in media with ≤ 40 mM glucose, at higher initial glucose concentrations, residual glucose values were anomalously high. This anomaly caused by hydrogen peroxide produced by the lactobacilli. Preincubating samples with catalase removed the endogenous hydrogen peroxide and resulted in accurate residual glucose values. The presence of catalase did not interfere with the subsequent peroxidase portion of the assay.     

Induction of a Futile Embden-Meyerhof-Parnas Pathway in Deinococcus radiodurans by Mn: Possible Role of the Pentose Phosphate Pathway in Cell Survival

Statistical models were used to predict the effects of tryptone, glucose, yeast extract (TGY) and Mn on biomass formation of the highly radioresistant bacterium Deinococcus radiodurans. Results suggested that glucose had marginal effect on biomass buildup, but Mn was a significant factor for biomass formation. Mn also facilitated glucose interactions with other nutrient components. These predictions were verified by in vivo and in vitro experiments. TGY-grown cells metabolized glucose solely by the pentose phosphate pathway (PPP). Although only a fraction of glucose from the medium was transported into the cells, glucose was incorporated into the DNA efficiently after cells were exposed to UV light. The presence of glucose also enhanced the radioresistance of the culture. Mn could induce an Embden-Meyerhof-Parnas (EMP) pathway in D. radiodurans. The EMP pathway and the PPP of the Mn-treated cells oxidized glucose simultaneously at a 6:1 ratio. Although glucose was hydrolyzed rapidly by the Mn-treated cells, most glucose was released as CO₂. Mn-treated cultures retained less glucose per cell than cells grown without Mn, and still less glucose was incorporated into the DNA after cells were exposed to UV light. Mn-treated cells were also more sensitive to UV light. Results suggested that metabolites of glucose generated from the PPP enhanced the survival of D. radiodurans. Induction of the EMP pathway by Mn may deplete metabolites for DNA repair and may induce oxidative stress for the cell, leading to reduction of radioresistance.     

Hxt-Carrier-Mediated Glucose Efflux upon Exposure of Saccharomyces cerevisiae to Excess Maltose

When wild-type Saccharomyces cerevisiae strains pregrown in maltose-limited chemostat cultures were exposed to excess maltose, release of glucose into the external medium was observed. Control experiments confirmed that glucose release was not caused by cell lysis or extracellular maltose hydrolysis. To test the hypothesis that glucose efflux involved plasma membrane glucose transporters, experiments were performed with an S. cerevisiae strain in which all members of the hexose transporter (HXT) gene family had been eliminated and with an isogenic reference strain. Glucose efflux was virtually eliminated in the hexose-transport-deficient strain. This constitutes experimental proof that Hxt transporters facilitate export of glucose from S. cerevisiae cells. After exposure of the hexose-transport-deficient strain to excess maltose, an increase in the intracellular glucose level was observed, while the concentrations of glucose 6-phosphate and ATP remained relatively low. These results demonstrate that glucose efflux can occur as a result of uncoordinated expression of the initial steps of maltose metabolism and the subsequent reactions in glucose dissimilation. This is a relevant phenomenon for selection of maltose-constitutive strains for baking and brewing.     

Identification of Glucose Transporters in Aspergillus nidulans

To characterize the mechanisms involved in glucose transport, in the filamentous fungus Aspergillus nidulans, we have identified four glucose transporter encoding genes hxtB-E. We evaluated the ability of hxtB-E to functionally complement the Saccharomyces cerevisiae EBY.VW4000 strain that is unable to grow on glucose, fructose, mannose or galactose as single carbon source. In S. cerevisiae HxtB-E were targeted to the plasma membrane. The expression of HxtB, HxtC and HxtE was able to restore growth on glucose, fructose, mannose or galactose, indicating that these transporters accept multiple sugars as a substrate through an energy dependent process. A tenfold excess of unlabeled maltose, galactose, fructose, and mannose were able to inhibit glucose uptake to different levels (50 to 80 %) in these s. cerevisiae complemented strains. Moreover, experiments with cyanide-m-chlorophenylhydrazone (CCCP), strongly suggest that hxtB, -C, and –E mediate glucose transport via active proton symport. The A. nidulans ΔhxtB, ΔhxtC or ΔhxtE null mutants showed ~2.5-fold reduction in the affinity for glucose, while ΔhxtB and -C also showed a 2-fold reduction in the capacity for glucose uptake. The ΔhxtD mutant had a 7.8-fold reduction in affinity, but a 3-fold increase in the capacity for glucose uptake. However, only the ΔhxtB mutant strain showed a detectable decreased rate of glucose consumption at low concentrations and an increased resistance to 2-deoxyglucose.     

Molecular mechanism of interaction of Mycobacterium tuberculosis with host macrophages under high glucose conditions

Mycobacterium tuberculosis has the potential to escape various cellular defense mechanisms for its survival which include various oxidative stress responses, inhibition of phagosome-lysosomes fusion and alterations in cell death mechanisms of host macrophages that are crucial for its infectivity and dissemination. Diabetic patients are more susceptible to developing tuberculosis because of impairement of innate immunity and prevailing higher glucose levels. Our earlier observations have demonstrated alterations in the protein profile of M. tuberculosis exposed to concurrent high glucose and tuberculosis conditions suggesting a crosstalk between host and pathogen under high glucose conditions. Since high glucose environment plays crucial role in the interaction of mycobacterium with host macrophages which provide a niche for the survival of M. tuberculosis, it is important to understand various interactive mechanisms under such conditions. Initial phagocytosis and containment of M. tuberculosis by macrophages, mode of macrophage cell death, respiratory burst responses, Mycobacterium and lysosomal co-localization were studied in M. tuberculosis H37Rv infected cells in the presence of varied concentrations of glucose in order to mimic diabetes like conditions. It was observed that initial attachment, phagocytosis and later containment were less effective under high glucose conditions in comparison to normal glucose. Mycobacterium infected cells showed more necrosis than apoptosis as cell death mechanism during the course of infection under high glucose concentrations. Co-localization and respiratory burst assay also indicated evasion strategies adopted by M. tuberculosis under such conditions. This study by using THP1 macrophage model of tuberculosis and high glucose conditions showed immune evasion strategies adapted during co-pathogenesis of tuberculosis and diabetes.     

Elevated Paracellular Glucose Flux across Cystic Fibrosis Airway Epithelial Monolayers Is an Important Factor for Pseudomonas aeruginosa Growth

People with cystic fibrosis (CF) who develop related diabetes (CFRD) have accelerated pulmonary decline, increased infection with antibiotic-resistant Pseudomonas aeruginosa and increased pulmonary exacerbations. We have previously shown that glucose concentrations are elevated in airway surface liquid (ASL) of people with CF, particularly in those with CFRD. We therefore explored the hypotheses that glucose homeostasis is altered in CF airway epithelia and that elevation of glucose flux into ASL drives increased bacterial growth, with an effect over and above other cystic fibrosis transmembrane conductance regulator (CFTR)-related ASL abnormalities. The aim of this study was to compare the mechanisms governing airway glucose homeostasis in CF and non-CF primary human bronchial epithelial (HBE) monolayers, under normal conditions and in the presence of Ps. aeruginosa filtrate. HBE-bacterial co-cultures were performed in the presence of 5 mM or 15 mM basolateral glucose to investigate how changes in blood glucose, such as those seen in CFRD, affects luminal Ps. aeruginosa growth. Calu-3 cell monolayers were used to evaluate the potential importance of glucose on Ps. aeruginosa growth, in comparison to other hallmarks of the CF ASL, namely mucus hyperviscosity and impaired CFTR-dependent fluid secretions. We show that elevation of basolateral glucose promotes the apical growth of Ps. aeruginosa on CF airway epithelial monolayers more than non-CF monolayers. Ps. aeruginosa secretions elicited more glucose flux across CF airway epithelial monolayers compared to non-CF monolayers which we propose increases glucose availability in ASL for bacterial growth. In addition, elevating basolateral glucose increased Ps. aeruginosa growth over and above any CFTR-dependent effects and the presence or absence of mucus in Calu-3 airway epithelia-bacteria co-cultures. Together these studies highlight the importance of glucose as an additional factor in promoting Ps. aeruginosa growth and respiratory infection in CF disease.     

Transport and Metabolism of Lactose, Glucose, and Galactose in Homofermentative Lactobacilli

A number of species of lactobacilli were examined for their ability to ferment both the glucose and galactose moieties of lactose. Lactobacillus helveticus strains metabolized both the glucose and galactose moieties, whereas L. bulgaricus, L. lactis, and L. acidophilus strains metabolized only the glucose moiety and released galactose into the growth medium. All four species tested contained β-galactosidase activity, and no significant phospho-β-galactosidase activity was observed. L. bulgaricus and L. helveticus had a phosphoenolpyruvate (PEP):glucose phosphotransferase system for the uptake of glucose, but no evidence for a PEP:lactose phosphotransferase or PEP:galactose phosphotransferase system was obtained.     

Investigation of ptsG gene in response to xylose utilization in Corynebacterium glutamicum

Corynebacterium glutamicum strains NC-2 were able to grow on xylose as sole carbon sources in our previous work. Nevertheless, it exhibited the major shortcoming that the xylose consumption was repressed in the presence of glucose. So far, regarding C. glutamicum, there are a number of reports on ptsG gene, the glucose-specific transporter, involved in glucose metabolism. Recently, we found ptsG had influence on xylose utilization and investigated the ptsG gene in response to xylose utilization in C. glutamicum with the aim to improve xylose consumption and simultaneously utilized glucose and xylose. The ptsG-deficient mutant could grow on xylose, while exhibiting noticeably reduced growth on xylose as sole carbon source. A mutant deficient in ptsH, a general PTS gene, exhibited a similar phenomenon. When complementing ptsG gene, the mutant ΔptsG-ptsG restored the ability to grow on xylose similarly to NC-2. These indicate that ptsG gene is not only essential for metabolism on glucose but also important in xylose utilization. A ptsG-overexpressing recombinant strain could not accelerate glucose or xylose metabolism. When strains were aerobically cultured in a sugar mixture of glucose and xylose, glucose and xylose could not be utilized simultaneously. Interestingly, the ΔptsG strain could co-utilize glucose and xylose under oxygen-deprived conditions, though the consumption rate of glucose and xylose dramatically declined. It was the first report of ptsG gene in response to xylose utilization in C. glutamicum.     

The effect of maintenance in vitro on glucose uptake and the incorporation of glucose into glycogen by adult Schistosoma mansoni

The effect of maintenance in vitro on glucose uptake and the incorporation of glucose into glycogen by adult Schistosoma mansoni. International Journal for Parasitology16: 253–261. Adult male Schistosoma mansoni rapidly depleted their glycogen reserves in vitro. Both sexes also exhibited a gradual reduction in glycogen content during prolonged maintenance. Paired and separated worms were incubated in [³H] glucose and rates of glucose uptake and incorporation into glycogen were determined following periods of maintenance in vitro. The glucose uptake rate declined during long-term maintenance and was higher for separated males and females than for equivalent paired worms. Increasing the medium glucose concentration also increased the rate of uptake. Glucose continued to be incorporated into glycogen throughout 10 days in vitro, with evidence from paired schistosomes suggesting that the rapid depletion of male glycogen could be due to a decrease in incorporation rate in vitro. The incubation of separated worms and the use of higher glucose concentrations in media both effected an increase in incorporation rate. These results are discussed in the light of observations of the depletion of schistosome glycogen in vitro.     

Antidiabetic,Antihyperlipidemic and Antioxidant Activities of a Novel Proteoglycan from Ganoderma Lucidum Fruiting Bodies on db/db Mice and the Possible Mechanism

Previously, we screened a proteoglycan for anti-hyperglycemic, named FYGL, from Ganoderma Lucidum. For further research of the antidiabetic mechanisms of FYGL in vivo, the glucose homeostasis, activities of insulin-sensitive enzymes, glucose transporter expression and pancreatic function were analyzed using db/db mice as diabetic models in the present work. FYGL not only lead to a reduction in glycated hemoglobin level, but also an increase in insulin and C-peptide level, whereas a decrease in glucagons level and showed a potential for the remediation of pancreatic islets. FYGL also increased the glucokinase activities, and simultaneously lowered the phosphoenol pyruvate carboxykinase activities, accompanied by a reduction in the expression of hepatic glucose transporter protein 2, while the expression of adipose and skeletal glucose transporter protein 4 was increased. Moreover, the antioxidant enzyme activities were also increased by FYGL treatment. Thus, FYGL was an effective antidiabetic agent by enhancing insulin secretion and decreasing hepatic glucose output along with increase of adipose and skeletal muscle glucose disposal in the late stage of diabetes. Furthermore, FYGL is beneficial against oxidative stress, thereby being helpful in preventing the diabetic complications.     

Relationship between blood glucose levels and hepatic Fto mRNA expression in mice

Common variants in the fat mass and obesity associated (FTO) gene are associated with obesity and type 2 diabetes. Fto-deficient mice develop hepatic insulin resistance, leading to the hypothesis that hepatic Fto plays a role in the regulation of glucose metabolism and that hepatic Fto expression is regulated by metabolic states. We found that hepatic Fto mRNA levels were increased by fasting in mice. Intraperitoneal glucose injection reduced hepatic Fto mRNA levels without significant changes in body weight in fasted mice. The inverse correlation between Fto mRNA and glucose remained significant after adjusting for body weight. There were positive correlations between hepatic Fto mRNA expression and gluconeogenic gene expression. These data support the hypothesis that hepatic Fto expression changes in response to metabolic states and glucose reduces hepatic Fto mRNA expression independently of body weight. Hepatic Fto may participate in the feedback regulation of glucose metabolism via gluconeogenesis.     

Substrate Preference in a Strain of Megasphaera elsdenii, a Ruminal Bacterium, and Its Implications in Propionate Production and Growth Competition

The NIAH 1102 strain of Megasphaera elsdenii utilized lactate in preference to glucose when the two substrates were present. Even when lactate was supplied to cells fermenting glucose, the cells switched substrate utilization from glucose to lactate and did not utilize glucose until lactate decreased to a low concentration (1 to 2 mM). Since substrate utilization was shifted gradually without intermittence, typical diauxic growth was not seen. The cyclic AMP content did not rise markedly with the shift in substrate utilization, suggesting that this nucleotide is not involved in the regulation of the shift. It was unlikely that propionate was produced from glucose, which was explicable by the fact that lactate racemase activity dropped rapidly with the exhaustion of lactate and cells actively fermenting glucose did not possess this enzyme. A coculture experiment indicated that M. elsdenii NIAH 1102 is overcome by Streptococcus bovis JB1 in the competition for glucose, mainly because M. elsdenii NIAH 1102 is obliged to utilize lactate produced by S. bovis JB1; i.e., glucose utilization by M. elsdenii NIAH 1102 is suppressed by the coexistence of S. bovis JB1.     

Effects of the HIV Protease Inhibitor Ritonavir on GLUT4 Knock-out Mice

HIV protease inhibitors acutely block glucose transporters (GLUTs) in vitro, and this may contribute to altered glucose homeostasis in vivo. However, several GLUT-independent mechanisms have been postulated. To determine the contribution of GLUT blockade to protease inhibitor-mediated glucose dysregulation, the effects of ritonavir were investigated in mice lacking the insulin-sensitive glucose transporter GLUT4 (G4KO). G4KO and control C57BL/6J mice were administered ritonavir or vehicle at the start of an intraperitoneal glucose tolerance test and during hyperinsulinemic-euglycemic clamps. G4KO mice exhibited elevated fasting blood glucose compared with C57BL/6J mice. Ritonavir impaired glucose tolerance in control mice but did not exacerbate glucose intolerance in G4KO mice. Similarly, ritonavir reduced peripheral insulin sensitivity in control mice but not in G4KO mice. Serum insulin levels were reduced in vivo in ritonavir-treated mice. Ritonavir reduced serum leptin levels in C57BL/6J mice but had no effect on serum adiponectin. No change in these adipokines was observed following ritonavir treatment of G4KO mice. These data confirm that a primary effect of ritonavir on peripheral glucose disposal is mediated through direct inhibition of GLUT4 activity in vivo. The ability of GLUT4 blockade to contribute to derangements in the other molecular pathways that influence insulin sensitivity remains to be determined.