Site fertility and soil water-table level affect fungal biomass production and community composition in boreal peatland forests

A substantial amount of below-ground carbon (C) is suggested to be associated with fungi, which may significantly affect the soil C balance in forested ecosystems. Ergosterol from in-growth mesh bags and litterbags was used to estimate fungal biomass production and community composition in drained peatland forests with differing fertility. Extramatrical mycelia (EMM) biomass production was generally higher in the nutrient-poor site, increased with deeper water table level and decreased along the length of the recovery time. EMM biomass production was of the same magnitude as in mineral-soil forests. Saprotrophic fungal biomass production was higher in the nutrient-rich site. Both ectomycorrhizal (ECM) and saprotrophic fungal community composition changed according to site fertility and water table level. ECM fungal community composition with different exploration types may explain the differences in fungal biomass production between peatland forests. Melanin-rich Hyaloscypha may indicate decreased turnover of biomass in nutrient-rich young peatland forest. Genera Lactarius and Laccaria may be important in nutrient rich and Piloderma in the nutrient-poor conditions, respectively. Furthermore, Paxillus involutus and Cortinarius sp. may be important generalists in all sites and responsible for EMM biomass production during the first summer months. Saprotrophs showed a functionally more diverse fungal community in the nutrient-rich site.     

Metabolic regulation in progression to autoimmune diabetes

Recent evidence from serum metabolomics indicates that specific metabolic disturbances precede β-cell autoimmunity in humans and can be used to identify those children who subsequently progress to type 1 diabetes. The mechanisms behind these disturbances are unknown. Here we show the specificity of the pre-autoimmune metabolic changes, as indicated by their conservation in a murine model of type 1 diabetes. We performed a study in non-obese prediabetic (NOD) mice which recapitulated the design of the human study and derived the metabolic states from longitudinal lipidomics data. We show that female NOD mice who later progress to autoimmune diabetes exhibit the same lipidomic pattern as prediabetic children. These metabolic changes are accompanied by enhanced glucose-stimulated insulin secretion, normoglycemia, upregulation of insulinotropic amino acids in islets, elevated plasma leptin and adiponectin, and diminished gut microbial diversity of the Clostridium leptum group. Together, the findings indicate that autoimmune diabetes is preceded by a state of increased metabolic demands on the islets resulting in elevated insulin secretion and suggest alternative metabolic related pathways as therapeutic targets to prevent diabetes.     

The ectomycorrhizal fungus Tricholoma matsutake is a facultative saprotroph in vitro

Tricholoma matsutake is an economically important ectomycorrhizal fungus of coniferous woodlands. Mycologists suspect that this fungus is also capable of saprotrophic feeding. In order to evaluate this hypothesis, enzyme and chemical assays were performed in the field and laboratory. From a natural population of T. matsutake in southern Finland, samples of soil-mycelium aggregate (shiro) were taken from sites of sporocarp formation and nearby control (PCR-negative) spots. Soil organic carbon and activity rates of hemicellulolytic enzymes were measured. The productivity of T. matsutake was related to the amount of utilizable organic carbon in the shiro, where the activity of xylosidase was significantly higher than in the control sample. In the laboratory, sterile pieces of bark from the roots of Scots pine were inoculated with T. matsutake and the activity rates of two hemicellulolytic enzymes (xylosidase and glucuronidase) were assayed. Furthermore, a liquid culture system showed how T. matsutake can utilize hemicellulose as its sole carbon source. Results linked and quantified the general relationship between enzymes secreted by T. matsutake and the degradation of hemicellulose. Our findings suggest that T. matsutake lives mainly as an ectomycorrhizal symbiont but can also feed as a saprotroph. A flexible trophic ecology confers T. matsutake with a clear advantage in a heterogeneous environment and during sporocarp formation.     

Pseudoxanthomonas bacteria that drive deposit formation of wood extractives can be flocculated by cationic polyelectrolytes

Runnability problems caused by suspended bacteria in water using industries, have, in contrast to biofilms, received little attention. We describe here that Pseudoxanthomonas taiwanensis, a wide-spread and abundant bacterium in paper machine water circuits, aggregated dispersions of wood extractives ("pitch") and resin acid, under conditions prevailing in machine water circuits (10⁹ cfu ml⁻¹, pH 8, 45°C). The aggregates were large enough (up to 50 μm) so that they could be expected to clog wires and felts and to reduce dewatering of the fiber web. The Pseudoxanthomonas bacteria were negatively charged over a pH range of 3.2–10. Cationic polyelectrolytes of the types used as retention aids or fixatives to flocculate "anionic trash" in paper machines were effective in flocculating the Pseudoxanthomonas bacteria. The polyelectrolyte most effective for this purpose was of high molecular weight (7–8 × 10⁶ g mol⁻¹) and low charge density (1 meq g⁻¹), whereas polyelectrolytes that effectively zeroed the electrophoretic mobility (i.e., neutralized the negative charge) of the bacterium were less effective in flocculating the bacteria. Based on the results, we concluded that the polyelectrolytes functioning by bridging mechanism, rather than by neutralization of the negative charge, may be useful as tools for reducing harmful deposits resulting from interaction of bacteria with wood extractives in warm water industry.     

Kinetics of prolonged photoinhibition revisited: photoinhibited Photosystem II centres do not protect the active ones against loss of oxygen evolution

Photoinhibition of Photosystem II (PSII) in lincomycin-treated leaves begins as a first-order reaction, but fluorescence measurements have suggested that after prolonged illumination, the number of active PSII centres stabilizes to 15–20% of control. The stabilization has been interpreted to indicate that photoinhibited PSII centres protect the remaining active centres against photoinhibition (Lee, Hong and Chow, Planta 212:332–342, 2001). In an attempt to study the mechanism of this protection, we measured the reaction kinetics of photoinhibition in lincomycin-treated pumpkin (Cucurbita pepo L.) and pepper (Capsicum annuum L.) leaves in vivo. The light-saturated rate of PSII oxygen evolution, assayed from thylakoids and isolated from the treated leaves, was used as a direct measure of the number of remaining active PSII centres, and the fluorescence parameters F _V/F _M and (F _V/F _M)/F ₀ (=1/F ₀ − 1/F _M) were measured for comparison. To our surprise, no stabilization of PSII activity was observed and photoinhibition followed first-order kinetics until PSII activity had virtually declined to zero. A series of in vitro experiments was carried out to see whether stabilization of PSII activity occurs if a particular combination of light intensity and wavelength range is applied, or if a specific PSII preparation is used as experimental material. The results of the in vitro experiments confirmed the in vivo result about persistent first-order kinetics. We conclude that photoinhibited PSII centres offer no measurable protection against photoinhibition.     

Sex Differences in Liver Toxicity—Do Female and Male Human Primary Hepatocytes React Differently to Toxicants In Vitro?

There is increasing amount of evidence for sex variation in drug efficiency and toxicity profiles. Women are more susceptible than men to acute liver injury from xenobiotics. In general, this is attributed to sex differences at a physiological level as well as differences in pharmacokinetics and pharmacodynamics, but neither of these can give a sufficient explanation for the diverse responses to xenobiotics. Existing data are mainly based on animal models and limited data exist on in vitro sex differences relevant to humans. To date, male and female human hepatocytes have not yet been compared in terms of their responses to hepatotoxic drugs. We investigated whether sex-specific differences in acute hepatotoxicity can be observed in vitro by comparing hepatotoxic drug effects in male and female primary human hepatocytes. Significant sex-related differences were found for certain parameters and individual drugs, showing an overall higher sensitivity of female primary hepatocytes to hepatotoxicants. Moreover, our work demonstrated that high content screening is feasible with pooled primary human hepatocytes in suspension.