Investigation of the occurrence of xylan-xyloglucan complexes in the cell walls of olive pulp (Olea europaea)

Previously we reported the possible occurrence of a complex containing glucuronoxylan and xyloglucan in the cell walls of olive pulp. In order to investigate the nature of this complex, the 1 M KOH (1 °C)-soluble polysaccharides in which it was prevalent, were separated by graded ethanol precipitation followed by anionexchange chromatography. A slightly acidic fraction was obtained and, by methylation analysis, glycosidic linkages typical of both xylan and xyloglucan were detected. Two distinct populations of the xylan-xyloglucan complexes were resolved by gel-filtration chromatography (2000 and 100 kDa) and the structural features were determined by methylation analysis. Cross-linking of the xylan-xyloglucan moieties was investigated by digestion of the xylan component with a purified, specific, endoxylanase. Although only the xylan element was digested, as verified by methylation analysis, the molecular weight of the xyloglucan moiety was also reduced. This confirmed that the xylan and xyloglucan moieties were strongly attached. The occurrence and structure of the xylan-xyloglucan complexes in the olive pulp cell walls is discussed.     

Copper tolerance in bacteria requires the activation of multiple accessory pathways

Copper is a required micronutrient for bacteria and an essential cofactor for redox-active cuproenzymes. Yet, excess copper is extremely toxic, and is exploited as a bacteriocide in medical and biotechnological applications and also by the mammalian immune system. To evade copper toxicity, bacteria not only control intracellular copper homeostasis, but they must also repair the damage caused by excess copper. In this review, we summarize the bacterial cell-wide response to copper toxicity in Enterobacteria. Tapping into the abundant research data on two key organisms, Escherichia coli and Salmonella enterica, we show that copper resistance requires both the direct copper homeostatic response and also the indirect accessory pathways that deal with copper-induced damage. Since patterns of copper response are conserved through the Proteobacteria, we propose a cell-wide view of copper detoxification and copper tolerance that can be used to identify novel targets for copper-based antibacterial therapeutics.     

Expression of Mitochondrial Cytochrome C Oxidase Chaperone Gene (COX20) Improves Tolerance to Weak Acid and Oxidative Stress during Yeast Fermentation

Introduction

Saccharomyces cerevisiae is the micro-organism of choice for the conversion of fermentable sugars released by the pre-treatment of lignocellulosic material into bioethanol. Pre-treatment of lignocellulosic material releases acetic acid and previous work identified a cytochrome oxidase chaperone gene (COX20) which was significantly up-regulated in yeast cells in the presence of acetic acid.

Results

A Δcox20 strain was sensitive to the presence of acetic acid compared with the background strain. Overexpressing COX20 using a tetracycline-regulatable expression vector system in a Δcox20 strain, resulted in tolerance to the presence of acetic acid and tolerance could be ablated with addition of tetracycline. Assays also revealed that overexpression improved tolerance to the presence of hydrogen peroxide-induced oxidative stress.

Conclusion

This is a study which has utilised tetracycline-regulated protein expression in a fermentation system, which was characterised by improved (or enhanced) tolerance to acetic acid and oxidative stress.     

Effect of macronutrients, age, and obesity on 6- and 24-h postprandial glucose metabolism in cats

Obesity and age are risk factors for feline diabetes. This study aimed to test the hypothesis that age, long-term obesity, and dietary composition would lead to peripheral and hepatorenal insulin resistance, indicated by higher endogenous glucose production (EGP) in the fasted and postprandial state, higher blood glucose and insulin, and higher leptin, free thyroxine, and lower adiponectin concentrations. Using triple tracer-(2)H(2)O, [U-(13)C(3)] propionate, and [3,4-(13)C(2)] glucose infusion, and indirect calorimetry-we investigated carbohydrate and fat metabolic pathways in overnight-fasted neutered cats (13 young lean, 12 old lean, and 12 old obese), each fed three different diets (high protein with and without polyunsaturated fatty acids, and high carbohydrate) in a crossover design. EGP was lowest in fasted and postprandial obese cats despite peripheral insulin resistance, indicated by hyperinsulinemia. Gluconeogenesis was the most important pathway for EGP in all groups, but glycogen contributed significantly. Insulin and leptin concentrations were higher in old than in young lean cats; adiponectin was lowest in obese cats but surprisingly highest in lean old cats. Diet had little effect on metabolic parameters. We conclude that hepatorenal insulin resistance does not develop in the fasted or postprandial state, even in long-term obese cats, allowing the maintenance of euglycemia through lowering EGP. Glycogen plays a major role in EGP, especially in lean fasted cats, and in the postprandial state. Aging may predispose to insulin resistance, which is a risk factor for diabetes in cats. Mechanisms underlying the high adiponectin of healthy old lean cats need to be further explored.