Range expansion and retraction along a moving contact zone has no effect on the genetic diversity of two passerine birds

Disentangling the factors shaping species distributions remains a central goal in biogeography, ecology and evolutionary biology. The extrinsic pressures that may facilitate range shifts, such as climatic factors or biotic interactions are well known. However, in contrast, the possible intrinsic factors are manifold and hard to generalize across taxa. Recently, several theoretical studies have investigated the consequences of moving range borders on genetic diversity. However, empirical studies that support or refute these theoretical predictions are scarce. Moving contact zones between parapatric sister species are suitable models to test these hypotheses. Changes in genetic diversity can be tested simultaneously along the expanding and receding edges of two species of the contact zone while accounting for intra‐specific effects (e.g. introgression). The two Old World warblers Hippolais polyglotta and H. icterina form a narrow moving contact zone, where interspecific interactions are suspected to be the main factor shaping this zone. We investigated the population genetic structure of both species along a transect ranging from the core range of the expanding H. polyglotta across the contact zone and far into the range of the receding H. icterina. The theoretical predictions of changes in genetic diversity at the range edges were tested. No gradual change in genetic diversity was detected for both the expanding and the receding range margin. Furthermore, no genetic structure was found in either species supporting the hypothesis that long distance dispersal (LDD) occurs frequently due to the high mobility of these long‐distance migrants. The results suggest that when dispersal propensity is high and accompanied by frequent LDD events, then neither an enrichment nor a depletion of alleles along moving range edges would be detected. This these species as the probability to retain genetic diversity during exogenous induced range shifts is high in such mobile species.     

Microcalorimetric Determination of the Thermostability of Three Hybrid (1–3,1–4)-β-Glucanases

Abstract

Thermodynamic parameters of the three hybrid (1–3,1–4)-β-glucanases H(A12-M), H(A12-M)ΔY13, and H(A16-M) composed of short N-terminal regions derived from the Bacillus amyloliquefaciens enzyme and a C-terminal region of the homologous Bacillus macerans enzyme were determined in 2mM sodium cacodylate pH 6.0,1.5 M guanidine hydrochloride, containing 1 mM CaCl₂ or 1 mM EDTA Melting of H(A12-M)ΔY13 and H(A16-M) in the presence of calcium ions is characterized by two subtransitions; only one transition is observed in the case of H(A12-M). In calcium-free buffer each of the three hybrid enzymes melts in one two-state transition. Transition temperatures T _m and molar enthalpy changes ΔH are reduced in the absence of calcium ions but the reduction is much more pronounced for H(A12-M)ΔY13 and H(A16-M) than for the less thermostable enzyme H(A12-M).     

Structural and functional reconstruction in situ of the [CuSMoO2] active site of carbon monoxide dehydrogenase from the carbon monoxide oxidizing eubacterium Oligotropha carboxidovorans

Carbon monoxide dehydrogenase from the bacterium Oligotropha carboxidovorans catalyzes the oxidation of CO to CO₂ at a unique [CuSMoO₂] cluster. In the bacteria the cluster is assembled post-translational. The integration of S, and particularly of Cu, is rate limiting in vivo, which leads to CO dehydrogenase preparations containing the mature and fully functional enzyme along with forms of the enzyme deficient in one or both of these elements. The active sites of mature and immature forms of CO dehydrogenase were converted into a [MoO₃] centre by treatment with potassium cyanide. We have established a method, which rescues 50% of the CO dehydrogenase activity by in vitro reconstitution of the active site through the supply of sulphide first and subsequently of Cu(I) under reducing conditions. Immature forms of CO dehydrogenase isolated from the bacterium, which were deficient in S and/or Cu at the active site, were similarly activated. X-ray crystallography and electron paramagnetic resonance spectroscopy indicated that the [CuSMoO₂] cluster was properly reconstructed. However, reconstituted CO dehydrogenase contains mature along with immature forms. The chemical reactions of the reconstitution of CO dehydrogenase are summarized in a model, which assumes resulphuration of the Mo-ion at both equatorial positions at a 1:1 molar ratio. One equatorial Mo–S group reacts with Cu(I) in a productive fashion yielding a mature, functional [CuSMoO₂] cluster. The other Mo–S group reacts with Cu(I), then Cu₂S is released and an oxo group is introduced from water, yielding an inactive [MoO₃] centre.     

Comparison of a xylanase and a complex of non starch polysaccharide-degrading enzymes with regard to performance and bacterial metabolism in weaned piglets

Weaned piglets were fed a wheat based diet either non-supplemented or supplemented with a multi-enzyme preparation or a xylanase mono-enzyme preparation, respectively. Both enzyme preparations increased live weight gain nonsignificantly, but only animals of the xylanase group showed a trend (p = 0.076) for an improved feed conversion. Only precaecal digestibility of total amino acids was improved significantly when the mono-enzyme preparation was added. Improvements of digestibility of crude fat, crude protein and starch did not reach the significance level. Both enzyme preparations reduced jejunal viscosity, however viscosity in the colon was only reduced by the mono-enzyme preparation. Both enzymes significantly reduced Lactobacillus spp. cell numbers as well as bacterial metabolites in the stomach and showed similar nonsignificant modifications in jejunum contents except for acetate in the mono-enzyme group. Total jejunal bile acids were unchanged. Compared to the control, the ratio of the main conjugated to the main deconjugated bile acid was significantly higher in the mono-enzyme group. This study has shown that the mono- and multi-enzyme preparation can lead to improved performance in wheat based diets for piglets. Like in poultry, the main mode of action seems to be the reduction of small intestinal viscosity. However, the generation of fermentable carbohydrates by the multi-enzyme preparation may mask beneficial effects on performance due to the development of an active bile acid deconjugating microbiota in the small intestine.     

Molybdenum-dependent sulfur oxidation in facultatively lithoautotrophic thiobacteria

Abstract The regulation of the synthesis of diaminopimelate decarboxylase (product of the lysA gene) of Escherichia coli was studied by measuring the expression of a lysA-lacZ chromosomal fusion. It appeared to be under an autogenous regulatory control involving lysine as an effector. The LysA protein from Pseudomonas aeruginosa could replace the E. coli protein in its regulatory role, but with a lower efficiency.     

The CoxD Protein,a Novel AAA+ ATPase Involved in Metal Cluster Assembly: Hydrolysis of Nucleotide-Triphosphates and Oligomerization

CoxD of the α-proteobacterium Oligotropha carboxidovorans is a membrane protein which is involved in the posttranslational biosynthesis of the [CuSMoO₂] cluster in the active site of the enzyme CO dehydrogenase. The bacteria synthesize CoxD only in the presence of CO. Recombinant CoxD produced in E. coli K38 pGP1-2/pETMW2 appeared in inclusion bodies from where it was solubilized by urea and refolded by stepwise dilution. Circular dichroism spectroscopy revealed the presence of secondary structural elements in refolded CoxD. CoxD is a P-loop ATPase of the AAA-protein family. Refolded CoxD catalyzed the hydrolysis of MgATP yielding MgADP and inorganic phosphate at a 1∶1∶1 molar ratio. The reaction was inhibited by the slow hydrolysable MgATP-γ-S. GTPase activity of CoxD did not exceed 2% of the ATPase activity. Employing different methods (non linear regression, Hanes and Woolf, Lineweaver-Burk), preparations of CoxD revealed a mean K_M value of 0.69±0.14 mM ATP and an apparent V_max value of 19.3±2.3 nmol ATP hydrolyzed min⁻¹ mg⁻¹. Sucrose density gradient centrifugation and gel filtration showed that refolded CoxD can exist in various multimeric states (2-mer, 4-mer or 6-mer), preferentially as hexamer or dimer. Within weeks the hexamer dissociates into the dimer, a process which can be reversed by MgATP or MgATP-γ-S within hours. Only the hexamers and the dimers exhibited MgATPase activity. Transmission electron microscopy of negatively stained CoxD preparations revealed distinct particles within a size range of 10–16 nm, which further corroborates the oligomeric organization. The 3D structure of CoxD was modeled with the 3D structure of BchI from Rhodobacter capsulatus as template. It has the key elements of an AAA+ domain in the same arrangement and at same positions as in BchI and displays the characteristic inserts of the PS-II-insert clade. Possible functions of CoxD in [CuSMoO₂] cluster assembly are discussed.