Generally applicable fed-batch culture concept based on the detection of metabolic state by on-line balancing

In many microorganisms, flux limitations in oxidative metabolism lead to the formation of overflow metabolites even under fully aerobic conditions. This can be avoided if the specific growth rate is controlled at a low enough value. This is usually accomplished by controlling the substrate feeding profile in a fed-batch process. The present work proposes a control concept which is based on the on-line detection of metabolic state by on-line calculation of mass and elemental balances. The advantages of this method are: 1) the check of measurement consistency based on all of the available measurements, 2) the minimum requirement of a priori knowledge of metabolism, and 3) the exclusive use of simple and established on-line techniques which do not require direct measurement of the metabolite in question. The control concept has been linked to a simple adaptive controller and applied to fed-batch cultures of S. cerevisiae and E. coli, organisms which express different overflow metabolites, ethanol and acetic acid, respectively. Oxidative and oxidoreductive states of S. cerevisiae and E. coli cultures were detected with high precision. As demonstrated by the formation of acetic acid in E. coli cultures, metabolic states could be correctly distinguished for systems for which traditional methods, such as respiratory quotient (RQ), are insensitive. Hence, it could be shown that the control concept allowed avoidance of overflow metabolite formation and operation at maximum oxidative biomass productivity and oxidative conversion of substrate into biomass. Based on mass and elemental balances, the proposed method additionally provides a richness of additional information, such as yield coefficients and estimation of concentrations and specific conversion rates. These data certainly help the operator to additionally evaluate the state of the process on-line.     

Regulation of hyphal growth and sporulation of the insect pathogenic fungus Entomophthora thripidum in vitro

Entomophthora thripidum is an obligate biotrophic insect pathogenic fungus that grows as protoplasts within the hemocoel of thrips. Prior to penetration through the insect cuticle and spore formation at the insect surface the protoplasts switch to hyphal growth. In vitro, the differentiation to hyphal growth was a prerequisite for the subsequent formation of infectious spores and was detected 10-20 days after inoculation. E. thripidum secreted a factor that autoinduced the differentiation to hyphal growth. The discovery of this activity inducing hyphal growth made possible the reliable production of spores, the infection of host insects and the consecutive re-isolation of the fungus from the infected insects.     

Carbohydrate metabolism is not impaired after 3 years of growth hormone therapy in children with Prader-Willi syndrome

BACKGROUND/AIM: In children with Prader-Labhart-Willi syndrome (PWS), the insulin secretion is reduced, despite obesity, being ascribed to the growth hormone (GH) deficiency of hypothalamic origin. Besides, an increased prevalence of diabetes mellitus was described in this syndrome. Hence, we addressed the questions of how body composition and insulin secretion are interrelated and what impact GH therapy has on the carbohydrate metabolism in PWS. METHODS: We measured weight, lean and fat mass (by dual-energy X-ray absorptiometry), triglycerides, HbA(1c), and fasting insulin and glucose levels in 17 children (age range 1.5-14.6 years) with PWS to examine whether the carbohydrate metabolism is altered during 36 months of therapy with 8 mg GH/m(2) body surface/week. In a subgroup of 8 children, the insulin secretion was longitudinally assayed during oral glucose tolerance at 0 and 12 months of therapy. RESULTS: Before therapy, the insulin secretion was lower and markedly delayed as compared with reference data and did not rise during therapy. The glucose tolerance was impaired in 2 of 12 children examined by oral glucose tolerance test before therapy and normalized during therapy. Fasting insulin and insulin resistance being normal at the beginning, significantly increased at 12 months and returned to initial levels at 36 months of GH therapy. Fasting glucose as well as HbA(1c) and triglyceride levels were always normal. The fat mass before GH therapy was increased (39.5%) and dropped into the upper normal range (28.3%) during 3 years of therapy, being correlated with fasting insulin concentration and indices of insulin sensitivity before and after 1 year of therapy. CONCLUSIONS: Children with PWS are characterized by an intact insulin sensitivity with a decrease and a delay of insulin secretion, regardless of moderate obesity or GH treatment. In the present setting, the carbohydrate metabolism is not impaired by GH therapy, but by the excessively increased fat mass.     

The citrate carrier CitS probed by single-molecule fluorescence spectroscopy

A prominent region of the Na(+)-dependent citrate carrier (CitS) from Klebsiella pneumoniae is the highly conserved loop X-XI, which contains a putative citrate binding site. To monitor potential conformational changes within this region by single-molecule fluorescence spectroscopy, the target cysteines C398 and C414 of the single-Cys mutants (CitS-sC398, CitS-sC414) were selectively labeled with the thiol-reactive fluorophores AlexaFluor 546/568 C(5) maleimide (AF(546), AF(568)). While both single-cysteine mutants were catalytically active citrate carriers, labeling with the fluorophore was only tolerated at C398. Upon citrate addition to the functional protein fluorophore conjugate CitS-sC398-AF(546), complete fluorescence quenching of the majority of molecules was observed, indicating a citrate-induced conformational change of the fluorophore-containing domain of CitS. This quenching was specific for the physiological substrate citrate and therefore most likely reflecting a conformational change in the citrate transport mechanism. Single-molecule studies with dual-labeled CitS-sC398-AF(546/568) and dual-color detection provided strong evidence for a homodimeric association of CitS.     

The pseudosclerotia of the agaric <Emphasis Type="Italic">Stropharia luteonitens</Emphasis>

Based on two Swiss collections, the structure of mature pseudosclerotia of Stropharia luteonitens (Basidiomycota, Hymenomycetes) is described for the first time. The difference between sclerotia and pseudosclerotia is discussed, and the uncertainty about the presence of such organs in Stropharia luteonitens is resolved.     

The phosphorylation of Ser318 of insulin receptor substrate 1 is not per se inhibitory in skeletal muscle cells but is necessary to trigger the attenuation of the insulin-stimulated signal

The Ser/Thr phosphorylation of insulin receptor substrate 1 (IRS) is one key mechanism to stimulate and/or attenuate insulin signal transduction. Using a phospho-specific polyclonal antibody directed against phosphorylated Ser(318) of IRS-1, we found a rapid and transient insulin-stimulated phosphorylation of Ser(318) in human and rodent skeletal muscle cell models and in muscle tissue of insulin-treated mice. None of the investigated insulin resistance-associated factors (e.g. high glucose, tumor necrosis factor-alpha, adrenaline) stimulated the phosphorylation of Ser(318). Studying the function of this phosphorylation, we found that replacing Ser(318) by alanine completely prevented both the attenuation of insulin-stimulated Akt/protein kinase B Ser(473) phosphorylation and glucose uptake after 60 min of insulin stimulation. Unexpectedly, after acute insulin stimulation, we observed that phosphorylation of Ser(318) is not inhibitory but rather enhances insulin signal transduction because introduction of Ala(318) led to a reduction of the insulin-stimulated Akt/protein kinase B phosphorylation. Furthermore, replacing Ser(318) by glutamate, i.e. mimicking phosphorylation, improved glucose uptake after acute insulin stimulation. These data suggest that phosphorylation of Ser(318) is not per se inhibitory but is necessary to trigger the attenuation of the insulin-stimulated signal in skeletal muscle cells. Investigating the molecular mechanism of insulin-stimulated Ser(318) phosphorylation, we found that phosphatidylinositol 3-kinase-mediated activation of atypical protein kinase C-zeta and recruitment of protein kinase C-zeta to IRS-1 was responsible for this phosphorylation. We conclude that Ser(318) phosphorylation of IRS-1 is an early physiological event in insulin-stimulated signal transduction, which attenuates the continuing action of insulin.