No abstract

Although fast-growing Populus species consume a large amount of water for biomass production, there are considerable variations in water use efficiency (WUE) across different poplar species. To compare differences in growth, WUE and anatomical properties of leaf and xylem and to examine the relationship between photosynthesis/WUE and anatomical properties of leaf and xylem, cuttings of six poplar species were grown in a botanical garden. The growth performance, photosynthesis, intrinsic WUE (WUE(i) ), stable carbon isotope composition (δ(13) C) and anatomical properties of leaf and xylem were analysed in these poplar plants. Significant differences were found in growth, photosynthesis, WUE(i) and anatomical properties among the examined species. Populus cathayana was the clone with the fastest growth and the lowest WUE(i) /δ(13) C, whereas P. × euramericana had a considerable growth increment and the highest WUE(i) /δ(13) C. Among the analysed poplar species, the highest total stomatal density in P. cathayana was correlated with its highest stomatal conductance (g(s) ) and lowest WUE(i) /δ(13) C. Moreover, significant correlations were observed between WUE(i) and abaxial stomatal density and stem vessel lumen area. These data suggest that photosynthesis, WUE(i) and δ(13) C are associated with leaf and xylem anatomy and there are tradeoffs between growth and WUE(i) . It is anticipated that some poplar species, e.g. P. × euramericana, are better candidates for water-limited regions and others, e.g. P. cathayana, may be better for water-abundant areas.

This experiment was conducted to investigate the effects of 1alpha-hydroxycholecalciferol (1alpha-OH D3) on the growth performance, tibia and plasma parameters, nutrient utilization, meat quality of the breast and thigh, and type IIb sodium phosphate cotranspoter gene expression of broilers. A total of 96 males of 1-d-old Arbor Acres broilers were randomly assigned to 8 cages of 12 birds each. Two dietary treatments were applied to 4 cages each. Diet 1 was prepared as the basal diet (nonphytate phosphorus, 0.21%), whereas diet 2 was the basal diet supplemented with 5 microg/kg of 1alpha-OH D3. Results showed that supplementation of the basal diet with 1alpha-OH D3 increased growth performance, tibia ash and strength, plasma inorganic phosphate concentration, utilization of total phosphorus and nonphytate phosphorus, lightness and yellowness of the breast and thigh meat, and intestinal type IIb sodium phosphate cotranspoter mRNA expression, whereas it decreased the shear force and water-holding capacity of the thigh meat. These data suggest that the addition of 1alpha-OH D3 might improve growth performance, tibia development, and meat quality in 1- to 21-d-old broilers by increasing the absorption and retention of phosphorus.

GH10 xylanase from Thermoascus aurantiacus strain SL16W (TasXyn10A) showed high stability and activity up to 70-75 °C. The enzyme's half-lives were 101 h, 65 h, 63 min and 6 min at 60, 70, 75 and 80 °C, respectively. The melting point (T m), as measured by DSC, was 78.5 °C, which is in line with a strong activity decrease at 75-80 °C. The biomass-dissolving ionic liquid 1-ethyl-3-methylimidazolium acetate ([emim]OAc) in 30 % concentration had a small effect on the stability of TasXyn10A; T m decreased by only 5 °C. It was also observed that [emim]OAc inhibited much less GH10 xylanase (TasXyn10A) than the studied GH11 xylanases. The K m of TasXyn10A increased 3.5-fold in 15 % [emim]OAc with xylan as the substrate, whereas the approximate level of V max was not altered. The inhibition of enzyme activity by [emim]OAc was lesser at higher substrate concentrations. Therefore, high solid concentrations in industrial conditions may mitigate the inhibition of enzyme activity by ionic liquids. Molecular docking experiments indicated that the [emim] cation has major binding sites near the catalytic residues but in lower amounts in GH10 than in GH11 xylanases. Therefore, [emim] cation likely competes with the substrate when binding to the active site. The docking results indicated why the effect is lower in GH10.

Under general aqueous conditions, xanthan appears in an ordered conformation, which makes its backbone largely resistant to degradation by known cellulases. Therefore, the xanthan degradation mechanism is still unclear because of the lack of an efficient hydrolase. Here, we report the catalytic properties of MiXen, a xanthan-degrading enzyme identified from the genus Microbacterium. MiXen is a 952-amino-acid protein that is unique to strain XT11. Both the sequence and structural features suggested that MiXen belongs to a new branch of the GH9 family and has a multimodular structure in which a catalytic (α/α)6 barrel is flanked by an N-terminal Ig-like domain and by a C-terminal domain that has very few homologues in sequence databases and functions as a carbohydrate-binding module (CBM). Based on circular dichroism, shear-dependent viscosity, and reducing sugar and gel permeation chromatography analysis, we demonstrated that recombinant MiXen efficiently and randomly cleaved glucosidic bonds within the highly ordered xanthan substrate. A MiXen mutant free of the C-terminal CBM domain partially lost its xanthan-hydrolyzing ability because of decreased affinity toward xanthan, indicating the CBM domain assisted MiXen in hydrolyzing highly ordered xanthan via recognizing and binding to the substrate. Furthermore, side chain substituents and the terminal mannosyl residue significantly influenced the activity of MiXen via the formation of barriers to enzymolysis. Overall, the results of this study provide insight into the hydrolysis mechanism and enzymatic properties of a novel endotype xanthanase that will benefit future applications. IMPORTANCE This work characterized a novel endotype xanthanase, MiXen, and elucidated that the C-terminal carbohydrate-binding module of MiXen could drastically enhance the hydrolysis activity of the enzyme toward highly ordered xanthan. Both the sequence and structural analysis demonstrated that the catalytic domain and carbohydrate-binding module of MiXen belong to the novel branch of the GH9 family and CBMs, respectively. This xanthan cleaver can help further reveal the enzymolysis mechanism of xanthan and provide an efficient tool for the production of molecular modified xanthan with new physicochemical and physiological functions.