Fructose metabolism in Chromohalobacter salexigens: interplay between the Embden–Meyerhof–Parnas and Entner–Doudoroff pathways

Background The halophilic bacterium Chromohalobacter salexigens metabolizes glucose exclusively through the Entner–Doudoroff (ED) pathway, an adaptation which results in inefficient growth, with significant carbon overflow, especially at low salinity. Preliminary analysis of C. salexigens genome suggests that fructose metabolism could proceed through the Entner–Doudoroff and Embden–Meyerhof–Parnas (EMP) pathways. In order to thrive at high salinity, this bacterium relies on the biosynthesis and accumulation of ectoines as major compatible solutes. This metabolic pathway imposes a high metabolic burden due to the consumption of a relevant proportion of cellular resources, including both energy molecules (NADPH and ATP) and carbon building blocks. Therefore, the existence of more than one glycolytic pathway with different stoichiometries may be an advantage for C. salexigens. The aim of this work is to experimentally characterize the metabolism of fructose in C. salexigens. Results Fructose metabolism was analyzed using in silico genome analysis, RT-PCR, isotopic labeling, and genetic approaches. During growth on fructose as the sole carbon source, carbon overflow was not observed in a wide range of salt concentrations, and higher biomass yields were reached. We unveiled the initial steps of the two pathways for fructose incorporation and their links to central metabolism. While glucose is metabolized exclusively through the Entner–Doudoroff (ED) pathway, fructose is also partially metabolized by the Embden–Meyerhof–Parnas (EMP) route. Tracking isotopic label from [1-13C] fructose to ectoines revealed that 81% and 19% of the fructose were metabolized through ED and EMP-like routes, respectively. Activities of enzymes from both routes were demonstrated in vitro by 31P-NMR. Genes encoding predicted fructokinase and 1-phosphofructokinase were cloned and the activities of their protein products were confirmed. Importantly, the protein encoded by csal1534 gene functions as fructose bisphosphatase, although it had been annotated previously as pyrophosphate-dependent phosphofructokinase. The gluconeogenic rather than glycolytic role of this enzyme in vivo is in agreement with the lack of 6-phosphofructokinase activity previously described. Conclusions Overall, this study shows that C. salexigens possesses a greater metabolic flexibility for fructose catabolism, the ED and EMP pathways contributing to a fine balancing of energy and biosynthetic demands and, subsequently, to a more efficient metabolism.University of Murcia and University of Seville was supported by projects: BIO2015-63949-R, BIO2014-54411-C2-1-REuropa MINECO/FEDER RTI2018-094393-B-C21Fundación Séneca (Grant no. 19236/PI/14

Fructose transport-deficient Staphylococcus aureus reveals important role of epithelial glucose transporters in limiting sugar-driven bacterial growth in airway surface liquid.

Hyperglycaemia as a result of diabetes mellitus or acute illness is associated with increased susceptibility to respiratory infection with Staphylococcus aureus. Hyperglycaemia increases the concentration of glucose in airway surface liquid (ASL) and promotes the growth of S. aureus in vitro and in vivo. Whether elevation of other sugars in the blood, such as fructose, also results in increased concentrations in ASL is unknown and whether sugars in ASL are directly utilised by S. aureus for growth has not been investigated. We obtained mutant S. aureus JE2 strains with transposon disrupted sugar transport genes. NE768(fruA) exhibited restricted growth in 10 mM fructose. In H441 airway epithelial-bacterial co-culture, elevation of basolateral sugar concentration (5-20 mM) increased the apical growth of JE2. However, sugar-induced growth of NE768(fruA) was significantly less when basolateral fructose rather than glucose was elevated. This is the first experimental evidence to show that S. aureus directly utilises sugars present in the ASL for growth. Interestingly, JE2 growth was promoted less by glucose than fructose. Net transepithelial flux of D-glucose was lower than D-fructose. However, uptake of D-glucose was higher than D-fructose across both apical and basolateral membranes consistent with the presence of GLUT1/10 in the airway epithelium. Therefore, we propose that the preferential uptake of glucose (compared to fructose) limits its accumulation in ASL. Pre-treatment with metformin increased transepithelial resistance and reduced the sugar-dependent growth of S. aureus. Thus, epithelial paracellular permeability and glucose transport mechanisms are vital to maintain low glucose concentration in ASL and limit bacterial nutrient sources as a defence against infection

High-fructose corn-syrup-sweetened beverage intake increases 5-hour breast milk fructose concentrations in lactating women

This study determined the effects of consuming a high-fructose corn syrup (HFCS)-sweetened beverage on breast milk fructose, glucose, and lactose concentrations in lactating women. At six weeks postpartum, lactating mothers (n = 41) were randomized to a crossover study to consume a commercially available HFCS-sweetened beverage or artificially sweetened control beverage. At each session, mothers pumped a complete breast milk expression every hour for six consecutive hours. The baseline fasting concentrations of breast milk fructose, glucose, and lactose were 5.0 ± 1.3 µg/mL, 0.6 ± 0.3 mg/mL, and 6.8 ± 1.6 g/dL, respectively. The changes over time in breast milk sugars were significant only for fructose (treatment × time, p < 0.01). Post hoc comparisons showed the HFCS-sweetened beverage vs. control beverage increased breast milk fructose at 120 min (8.8 ± 2.1 vs. 5.3 ± 1.9 µg/mL), 180 min (9.4 ± 1.9 vs. 5.2 ± 2.2 µg/mL), 240 min (7.8 ± 1.7 vs. 5.1 ± 1.9 µg/mL), and 300 min (6.9 ± 1.4 vs. 4.9 ± 1.9 µg/mL) (all p < 0.05). The mean incremental area under the curve for breast milk fructose was also different between treatments (14.7 ± 1.2 vs. −2.60 ± 1.2 µg/mL × 360 min, p < 0.01). There was no treatment × time interaction for breast milk glucose or lactose. Our data suggest that the consumption of an HFCS-sweetened beverage increased breast milk fructose concentrations, which remained elevated up to five hours post-consumption

The Use of an Anthrone Reagent to Detect Sugar Meals and Their Persistence in the Mosquito \u3ci\u3eAedes Triseriatus\u3c/i\u3e (Diptera: Culicidae)

Adults of Aedes triseriatus were fed water, blood, and 10% pure and mixed solutions of glucose, fructose and sucrose. Adults were tested for fructose by the cold-anthrone test 0, 1, 4, 12, and 24 h after feeding. Water-fed males and females and blood-fed females were anthrone negative. Glucose-fed males were anthrone negative but some glucose-fed females were weakly anthrone positive immediately after feeding. Many adults fed a mixture of glucose, fructose and sucrose were anthrone negative 12 h after feeding and all were anthrone negative after 24 h. The interpretation of negatives in the anthrone test is discussed with respect to the dynamics of nectar feeding, metabolic rates and sampling regimes

Utilizing Imogolite Nanotubes as a Tunable Catalytic Material for the Selective Isomerization of Glucose to Fructose

The isomerization of glucose to fructose is an important step in the conversion of biomass to valuable fuels and chemicals. A key challenge for the isomerization reaction is achieving high selectivity towards fructose using recyclable and inexpensive catalysts. Imogolite is a single-walled aluminosilicate nanotube characterized by surface areas of 200-400 m2/g and pore widths near 1 nm. In this study, imogolite nanotubes are used as a heterogeneous catalyst for the isomerization of glucose to fructose. Catalytic testing demonstrates the catalytic activity of imogolite for the isomerization of glucose to fructose. Imogolite is a highly tunable structure and can be modified through substitution of Si with Ge or through functionalization of methyl groups to the inner surface. These modifications change the surface properties of the nanotubes and enable tuning of the catalytic performance. Aluminosilicate imogolite is the most active material for the conversion of glucose. Conversion of glucose of 30% and selectivity for fructose of 45% is achieved using aluminosilicate imogolite. Modification of imogolite with germanium or methyl groups decreases the conversion, but increases the selectivity. Generally, the selectivity for fructose decreases as the conversion of glucose increases. Interestingly, the imogolite nanotubes have comparable catalytic selectivity at similar conversion as base catalyzed reactions. Catalyst recycling experiments revealed that organic content accumulates on the nanotubes that results in a minor reduction in conversion while maintaining similar catalytic selectivity. Overall, imogolite nanotubes demonstrate an active and tunable catalytic platform for the isomerization of glucose to fructose.American Chemical Society Petroleum Research Fund (ACS-PRF 55946-DNI5)National Science Foundation (NSF CBET 1605037; 1653587 and NSF CBET REU 1645126)Ohio State University Institute of Materials Research (OSU IMR FG0138)The Undergraduate Research Office and Office of ResearchA one-year embargo was granted for this item.Academic Major: Chemical Engineerin

Effect of cyclosporine on hepatic energy status and on fructose metabolism after portacaval shunt in dog as monitored by phosphorus‐31 nuclear magnetic resonance spectroscopy in vivo

The effect of cyclosporin A on the hepatic energy status and intracellular pH of the liver and its response to a fructose challenge has been investigated using in vivo phosphorus‐31 nuclear magnetic resonance spectroscopy in dogs. Three experimental groups were studied: (a) control dogs (n = 5), (b) dogs 4 days after the creation of an end‐to‐side portacaval shunt (n = 5), and (c) dogs 4 days after portacaval shunt and continuous infusion of cyclosporin A (4 mg/kg/day) by way of the left portal vein (portacaval shunt plus cyclosporin A, n = 5). The phosphorus‐31 nuclear magnetic resonance spectra were obtained at 81 MHz using a Bruker BIOSPEC II 4.7‐tesla nuclear magnetic resonance system equipped with a 40‐cm horizontal bore superconducting solenoid. The phosphomonoesters (p < 0.01), inorganic phosphate and ATP levels (p < 0.05) were decreased significantly in portacaval shunt–treated and in portacaval shunt‐pluscyclosporin A–treated dogs compared with unshunted control dogs. After a fructose challenge (750 mg/kg body wt, intravenously), fructose‐1‐phosphate metabolism was reduced in portacaval shunt–treated dogs compared with either the normal or portacaval shuntplus‐cyclosporin A–treated dogs (p < 0.05). Both portacaval shunt– and portacaval shunt‐plus‐cyclosporin A–treated dogs demonstrated a reduced decline in ATP levels after fructose infusion when compared with the controls (p < 0.05). Immediately after the fructose challenge, the intracellular pH decreased from 7.30 ± 0.03 to 7.00 ± 0.05 in all animals (p < 0.01) and then gradually returned to normal over 60 min. These data, obtained in vivo using phosphorus‐31 nuclear magnetic resonance spectroscopy of the liver after a portacaval shunt, suggest that: (a) the energy status of the liver is reduced in dogs with a portacaval shunt compared with that of normal controls and (b) cyclosporin A treatment ameliorates the reduction in hepatic metabolism normally observed after a fructose challenge to the liver with a portacaval shunt. (HEPATOLOGY 1991;13:780–785.) Copyright © 1991 American Association for the Study of Liver Disease

Protective Role of S-Adenosylmethionine Against Fructose-Induced Oxidative Damage in Obesity

Introduction. It has been shown that S-adenosylmethionine (S-AMe) stimulates glutathione synthesis and increases cell resistance to the cytotoxic action of free radicals and pro-inflammatory cytokines. The aim of this study was to determine the effect of S-adenosylmethionine on the oxidative stress in adipose tissue in a model of fructose-induced obesity. Methods. The study was performed on male Wistar rats divided into 3 groups: control, fructose fed (HFD) (35%, 16 weeks), and HFD + S-AMe (20 mg/kg). We examined the changes in the ratio of retroperitoneal adipose tissue weight / body weight; levels of reduced glutathione (GSH) and malondialdehyde (MDA) in the retroperitoneal adipose tissue, and serum levels of GSH and TNF-α. Results. Significant increases in the retroperitoneal adipose tissue, MDA, and serum TNF-α were identified, as well as decreased tissue and serum levels of GSH in rats fed with a high-fructose diet as compared with the control group. In the group fed with HFD and S-AMe, we found significant reduction in the retroperitoneal adipose tissue and decreased levels of MDA and serum TNF-α, as well as increased tissue and serum levels of GSH as compared with the group only on HFD. In conclusion, our results show that fructose-induced obesity causes oxidative stress in hypertrophic visceral adipose tissue. The administration of S-AMe improves the antioxidative protection of adipocytes, and reduces oxidative damage and excessive accumulation of lipids and inflammation