Characterization of two cellobiose dehydrogenases and comparison of their contributions to total activity in Neurospora crassa

Cellobiose dehydrogenase production by Neurospora crassa was investigated in this study. N. crassa has two putative cellobiose dehydrogenase (CDH) genes (cdh) in its genome. CDH was produced only under cellulolytic conditions. Deletion of nc-cdh1 eliminated almost all of the strain’s CDH activity, whereas the deletion of nc-cdh2 had little effect on total extracellular CDH activity, which indicates that NC-CDH1 is a major contributor to overall CDH activity. The homologous expression of nc-cdh1 and nc-cdh2 under the control of the constitutive D-glyceraldehyde-3-phosphate dehydrogenase (gpdA) promoter enabled recombinant CDH production under non-cellulolytic conditions. Both NC-CDH1 and NC-CDH2 produced by N. crassa were successfully purified and characterized for the first time. NC-CDH1 and NC-CDH2 have molecular weights of 100 kDa and 130 kDa, respectively. When their N-linked glycans were removed by N-glycosidase F treatment, both enzymes showed a molecular weight of 95 kDa. Although NC-CDH2 lacks the cellulose-binding module and contributed marginally to total CDH activity in N. crassa, NC-CDH2 has specific activity similar to that of NC-CDH1 (7.93 vs. 8.89 IU mg⁻¹), and it has a much lower K_m value than that of NC-CDH1 (5.79 vs. 25.72 μM). The lower activity contribution of NC-CDH2 in the wild-type strain may results from its lower enzyme production.     

Effect of different carbon and nitrogen sources on laccase and peroxidases production by selected Pleurotus species

Pleurotus eryngii, P. ostreatus and P. pulmonarius produced laccase (Lac) both under conditions of submerged fermentation (SF) and solid-state fermentation (SSF) with all of the investigated carbon and nitrogen sources. The highest levels of Lac activity were found in P. eryngii, under SF conditions of dry ground mandarine peels and in P. ostreatus, strain No. 493, under SSF conditions of grapevine sawdust.High levels of peroxidases activities were occurred in P. ostreatus, strain No. 494, and P. pulmonarius, under SSF conditions of grapevine sawdust, whereas in SF, these activities were either very low or absent.After purification of extracellular crude enzyme mixture of investigated species and strain which were grown in the medium with the best carbon sources, the Lac activity measurements revealed two peaks in P. eryngii, three peaks in both P. ostreatus strains and three in P. pulmonarius. Results obtained after purification also showed that the levels of phenol red oxidation in absence of external Mn²⁺ were higher than phenol red oxidation levels in presence of external Mn²⁺.In the medium with the best carbon sources (mandarine peels and grapevine sawdust, respectively), both P. eryngii and P. ostreatus, strain No. 493, showed the highest Lac activity with (NH₄)₂SO₄, as a nitrogen source, with a nitrogen concentration of 20 and 30 mM, respectively.In P. ostreatus, strain No. 494, and P. pulmonarius, the best nitrogen sources for peroxidases production were peptone in a concentration of 0.5% and NH₄NO₃ with a nitrogen concentration of 30 mM, respectively.     

Simulate the diffusion of hydrated ions by nanofiltration membrane process with random walk

We propose a new diffusion model describing the diffusion behaviours of hydrated ions in the process of nanofiltration (NF) based on the random walk (RW) theory when the NF membrane is uncharged or low charged. In this model, the hydration of ions and their deformation capacity are considered. The structure of the membrane is idealised into a lozenge shape and the diameter of membrane pore is defined as gapsize. A computer program named RW system in chemistry is developed to simulate based on this model. Six familiar ions Li⁺, Na⁺, Mg²⁺, Al³⁺, K⁺ and Ca²⁺ are investigated. Their characteristics are calculated by Gaussian 03, Pople, Inc., Wallingford, CT. The diffusivities of hydrated ions are calculated and discussed. The results show that the hydration of ions cannot be ignored in NF process when the membrane pore size is near the dimensions of the hydrated ions.     

Recent advances on the difructose anhydride IV preparation from levan conversion

Applied Microbiology and Biotechnology - Difructose anhydride IV (DFA IV) is a cyclic disaccharide consisting of two fructose residues, which is obtained from levan conversion with levan...     

Nesfatin-1 inhibits voltage gated K+ channels in pancreatic beta cells

The anorexigenic neuropeptide NEFA/nucleobindin 2 (NUCB2)/nesfatin-1-containing neurons are distributed in the brain regions involved in feeding regulation. In spite of the growing knowledge of its physiological functions through extensive studies, its molecular mechanism of reaction, including its receptor, remains unknown. NUCB2/nesfatin-1 is also involved in various peripheral regulations, including glucose homeostasis. In pancreatic beta-cells, NUCB2/nesfatin-1 is reported to enhance glucose-stimulated insulin secretion (GSIS) but its exact mechanism remains unknown.To clarify this mechanism, we measured the effect of nesfatin-1 on the electrical activity of pancreatic beta-cells. Using mouse primary beta cells, we measured changes in the ATP-sensitive K⁺ (K_ATP) channel current, the voltage-gated K⁺ (Kv) channel current, and insulin secretion upon application of nesfatin-1.Nesfatin-1 inhibited the Kv channel, but K_ATP channel activity was unaffected. Nesfatin-1 enhanced insulin secretion to a same level as Kv channel blocker tetraethylammonium (TEA). The effect was not further enhanced when nesfatin-1 and TEA were applied simultaneously. The inhibition binding assay with [¹²⁵I]nesfatin-1 in Kv2.1 channels, major contributor of Kv current in beta cell, expressing HEK239 cells indicated the binding of nesfatin-1 on Kv2.1 channel.Because Kv channel inhibition enhances insulin secretion under high glucose conditions, our present data suggest a possible mechanism of nesfatin-1 on enhancing GSIS through regulation of ion channels rather than its unidentified receptor.     

DNA barcoding of Chinese snakes reveals hidden diversity and conservation needs

DNA barcoding has greatly facilitated studies of taxonomy, biodiversity, biological conservation, and ecology. Here, we establish a reliable DNA barcoding library for Chinese snakes, unveiling hidden diversity with implications for taxonomy, and provide a standardized tool for conservation management. Our comprehensive study includes 1638 cytochrome c oxidase subunit I (COI) sequences from Chinese snakes that correspond to 17 families, 65 genera, 228 named species (80.6% of named species) and 36 candidate species. A barcode gap analysis reveals gaps, where all nearest neighbour distances exceed maximum intraspecific distances, in 217 named species and all candidate species. Three species-delimitation methods (ABGD, sGMYC, and sPTP) recover 320 operational taxonomic units (OTUs), of which 192 OTUs correspond to named and candidate species. Twenty-eight other named species share OTUs, such as Azemiops feae and A. kharini, Gloydius halys, G. shedaoensis, and G. intermedius, and Bungarus multicinctus and B. candidus, representing inconsistencies most probably caused by imperfect taxonomy, recent and rapid speciation, weak taxonomic signal, introgressive hybridization, and/or inadequate phylogenetic signal. In contrast, 43 species and candidate species assign to two or more OTUs due to having large intraspecific distances. If most OTUs detected in this study reflect valid species, including the 36 candidate species, then 30% more species would exist than are currently recognized. Several OTU divergences associate with known biogeographic barriers, such as the Taiwan Strait. In addition to facilitating future studies, this reliable and relatively comprehensive reference database will play an important role in the future monitoring, conservation, and management of Chinese snakes.     

Gymnoascus arxii's potential in deteriorating woollen textiles dyed with natural and synthetic dyes

So far, very little is known about microbiological deterioration of dyed woollen textiles. In this paper, the influence of the Gymnoascus arxii fungus on woollen textiles dyed with natural and synthetic dyes was studied. What is more, it was analysed whether the enrichment of the culture medium with additional nutrients has any impact on the deterioration of dyed woollen fabrics caused by a strongly keratinolytic strain. The study was carried out by means of a pure culture method over three different time periods, i.e. 1, 2 and 4 weeks. Within a week, the pure Gymnoascus arxii strain led to a severe deterioration in the mechanical strength of the examined woollen textiles, with the raw fabric being the most severely damaged. After the two-week incubation period, only the fabrics coloured in yellow, i.e. the fabric dyed with natural dye weld, and the synthetic yellow textile as well as the textile dyed with natural dye indigo survived, exclusively on the enriched medium. Solely the weld dyed textile withstood the four-week culture on the nutrient-enriched medium. The conducted studies demonstrated a strong influence of Gymnoascus arxii on dyed fabrics leading to their irreversible destruction. It has been also shown that the presence of nutrients in the substrate that are readily available to microorganism may hinder the development of the Gymnoascus arxii strain and thus, prevent textile deterioration.     

Isoprenoid emissions,photosynthesis and mesophyll diffusion conductance in response to blue light

The effects of blue light (BL) on leaf gas exchange of Populus × canadensis, a strong isoprene emitter, and Quercus ilex and Citrus reticulata, two monoterpene emitters with respectively small and large storage pools for monoterpenes, were studied. Leaves were initially exposed to a saturating photosynthetic photon flux density (PPFD) of white light (WL), which was then progressively reduced to perform WL-response curves. Leaves acclimated to saturating WL were then quickly exposed to equivalent BL levels to perform BL-response curves. Blue light did not significantly affect photosynthetic parameters in the light-limited portion of the PPFD-response curves in both P. × canadensis and Q. ilex. Whereas photosynthesis (A), stomatal conductance (g_s), and mesophyll conductance (g_m) were significantly decreased at high PPFDs of BL. A was similarly inhibited by BL in C. reticulata, but there was no significant effect of light quality on g_s. Overall these results show that the negative effect of BL on photosynthesis is widespread in tree species with different leaf characteristics, and that this involves coordinated reductions in g_s and g_m. BL negatively affected isoprene emission and, to a lesser extent monoterpene emissions, in concert with photosynthetic inhibition. Interesting, both isoprene and monoterpene emissions were shown to be inversely dependent upon intercellular [CO₂]. These results indicate that a change in light spectral quality, which can vary during the day, between days and within seasons, can alter photosynthesis and isoprenoid emissions, depending on the PPFD intensity. Such effects should be strongly considered in photosynthesis and volatile isoprenoid emission models.     

Effects of external stimuli on the pacemaker function of the sinoatrial node in sodium channel gene mutations models

Loss of function and gain of function mutations of the sodium channel were investigated using an intact two-dimensional rabbit sinoatrial node (SAN) and atrial cell model. The effects of three external stimuli (acetylcholine secretion by the vagal nerve, acid-base concentration, and tissue temperature) on cardiac pacemaker function and conduction were studied. Our results show that these two groups of mutations have different effects on pacemaker function and conduction. Furthermore, we found that the negative effects of these mutations could be altered by external stimuli. The bradycardic effects of mutations were magnified by an increase in acetylcholine level. Changes in acid-base concentration and tissue temperature increased the ability of the SAN to recover its pacemaker function. The results of this study increase our understanding of sodium channel disorders, and help to advance research on the treatment of these conditions.