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181.
Accumulation of trans C18:1 Fatty Acids in the Rumen after Dietary Algal Supplementation Is Associated with Changes in the Butyrivibrio Community
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Charlotte Boeckaert Bruno Vlaeminck Veerle Fievez Lois Maignien Jan Dijkstra Nico Boon 《Applied microbiology》2008,74(22):6923-6930
Optimization of the fatty acid composition of ruminant milk and meat is desirable. Dietary supplementation of algae was previously shown to inhibit rumen biohydrogenation, resulting in an altered milk fatty acid profile. Bacteria involved in biohydrogenation belong to the Butyrivibrio group. This study was aimed at relating accumulation of biohydrogenation intermediates with shifts in Butyrivibrio spp. in the rumen of dairy cows. Therefore, an experiment was performed with three rumen-fistulated dairy cows receiving a concentrate containing algae (9.35 g/kg total dry matter [DM] intake) for 20 days. Supplementation of the diet with algae inhibited biohydrogenation of C18:2 omega 6 (n-6) and C18:3 n-3, resulting in increased concentrations of biohydrogenation intermediates, whereas C18:0 decreased. Addition of algae increased ruminal C18:1 trans fatty acid concentrations, mainly due to 6- and 20-fold increases in C18:1 trans 11 (t11) and C18:1 t10. The number of ciliates (5.37 log copies/g rumen digesta) and the composition of the ciliate community were unaffected by dietary algae. In contrast, supplementation of the diet with algae changed the composition of the bacterial community. Primers for the Butyrivibrio group, including the genera Butyrivibrio and Pseudobutyrivibrio, were specifically designed. Denaturing gradient gel electrophoresis showed community changes upon addition of algae without affecting the total amount of Butyrivibrio bacteria (7.06 log copies/g rumen DM). Clone libraries showed that algae affected noncultivated species, which cluster taxonomically between the genera Butyrivibrio and Pseudobutyrivibrio and might play a role in biohydrogenation. In addition, 20% of the clones from a randomly selected rumen sample were related to the C18:0-producing branch, although the associated C18:0 concentration decreased through supplementation of the diet with algae. 相似文献
182.
Rozeboom HJ Bjerkan TM Kalk KH Ertesvåg H Holtan S Aachmann FL Valla S Dijkstra BW 《The Journal of biological chemistry》2008,283(35):23819-23828
Alginate is a family of linear copolymers of (1-->4)-linked beta-d-mannuronic acid and its C-5 epimer alpha-l-guluronic acid. The polymer is first produced as polymannuronic acid and the guluronic acid residues are then introduced at the polymer level by mannuronan C-5-epimerases. The structure of the catalytic A-module of the Azotobacter vinelandii mannuronan C-5-epimerase AlgE4 has been determined by x-ray crystallography at 2.1-A resolution. AlgE4A folds into a right-handed parallel beta-helix structure originally found in pectate lyase C and subsequently in several polysaccharide lyases and hydrolases. The beta-helix is composed of four parallel beta-sheets, comprising 12 complete turns, and has an amphipathic alpha-helix near the N terminus. The catalytic site is positioned in a positively charged cleft formed by loops extending from the surface encompassing Asp(152), an amino acid previously shown to be important for the reaction. Site-directed mutagenesis further implicates Tyr(149), His(154), and Asp(178) as being essential for activity. Tyr(149) probably acts as the proton acceptor, whereas His(154) is the proton donor in the epimerization reaction. 相似文献
183.
Estimation of the stoichiometry of volatile fatty acid production in the rumen of lactating cows 总被引:2,自引:0,他引:2
Bannink A Kogut J Dijkstra J France J Kebreab E Van Vuuren AM Tamminga S 《Journal of theoretical biology》2006,238(1):36-51
The purpose of this study was to improve the prediction of the quantity and type of Volatile Fatty Acids (VFA) produced from fermented substrate in the rumen of lactating cows. A model was formulated that describes the conversion of substrate (soluble carbohydrates, starch, hemi-cellulose, cellulose, and protein) into VFA (acetate, propionate, butyrate, and other VFA). Inputs to the model were observed rates of true rumen digestion of substrates, whereas outputs were observed molar proportions of VFA in rumen fluid. A literature survey generated data of 182 diets (96 roughage and 86 concentrate diets). Coefficient values that define the conversion of a specific substrate into VFA were estimated meta-analytically by regression of the model against observed VFA molar proportions using non-linear regression techniques. Coefficient estimates significantly differed for acetate and propionate production in particular, between different types of substrate and between roughage and concentrate diets. Deviations of fitted from observed VFA molar proportions could be attributed to random error for 100%. In addition to regression against observed data, simulation studies were performed to investigate the potential of the estimation method. Fitted coefficient estimates from simulated data sets appeared accurate, as well as fitted rates of VFA production, although the model accounted for only a small fraction (maximally 45%) of the variation in VFA molar proportions. The simulation results showed that the latter result was merely a consequence of the statistical analysis chosen and should not be interpreted as an indication of inaccuracy of coefficient estimates. Deviations between fitted and observed values corresponded to those obtained in simulations. 相似文献
184.
Dijkstra PD Seehausen O Groothuis TG 《Proceedings. Biological sciences / The Royal Society》2008,275(1634):519-526
The maintenance of colour polymorphisms within populations has been a long-standing interest in evolutionary ecology. African cichlid fish contain some of the most striking known cases of this phenomenon. Intrasexual selection can be negative frequency dependent when males bias aggression towards phenotypically similar rivals, stabilizing male colour polymorphisms. We propose that where females are territorial and competitive, aggression biases in females may also promote coexistence of female morphs. We studied a polymorphic population of the cichlid fish Neochromis omnicaeruleus from Lake Victoria, in which three distinct female colour morphs coexist: one plain brown and two blotched morphs. Using simulated intruder choice tests in the laboratory, we show that wild-caught females of each morph bias aggression towards females of their own morph, suggesting that females of all three morphs may have an advantage when their morph is locally the least abundant. This mechanism may contribute to the establishment and stabilization of colour polymorphisms. Next, by crossing the morphs, we generated sisters belonging to different colour morphs. We find no sign of aggression bias in these sisters, making pleiotropy unlikely to explain the association between colour and aggression bias in wild fish, which is maintained in the face of gene flow. We conclude that female-female aggression may be one important force for stabilizing colour polymorphism in cichlid fish. 相似文献
185.
Within-clutch patterns of yolk testosterone vary with the onset of incubation in black-headed gulls 总被引:2,自引:0,他引:2
Muller Wendt; Eising Corine M.; Dijkstra Cor; Groothuis Ton G. G. 《Behavioral ecology》2004,15(6):893-397
Hatching asynchrony in birds produces an age and size hierarchyamong siblings. Later-hatching chicks have a competitive disadvantage,and brood reduction may occur when food availability is insufficientto raise all chicks. When early-hatched chicks fail to surviveor if the circumstances allow raising all chicks, mothers shouldreverse the disadvantage to later-hatched chicks. Increasingdeposition of maternal androgens with the laying sequence hasbeen suggested to compensate for detrimental effects of hatchingasynchrony, allowing a more precise adjustment of the survivalprobabilities of each chick. Here, we show for black-headedgulls that the increase in yolk testosterone with each successiveegg is greater when the mother incubates longer before clutchcompletion, which is the major determinant of the degree ofhatching asynchrony. This finding supports the idea that yolktestosterone has a compensatory function in the context of hatchingasynchrony. Our data further show that if the time needed tocomplete a clutch is lengthened, the developmental differencesdue to incubation between the first- and the last-laid eggsincrease. In addition, the onset of incubation before clutchcompletion occurs sooner as the breeding season progresses.Both long inter-egg intervals and the seasonal shift in incubationbehavior enhance the necessity of compensation for later-hatchingchicks. Indeed, yolk levels of testosterone increased more steeplyover the laying order, if the duration of the egg-laying periodwas extended and in later-laid clutches. We suggest that prolactinplays a key role in the adjustment of testosterone allocationto the incubation pattern. 相似文献
186.
Jochen BW Wolf Chris Harrod Sylvia Brunner Sandie Salazar Fritz Trillmich Diethard Tautz 《BMC evolutionary biology》2008,8(1):150
Background
Oceans are high gene flow environments that are traditionally believed to hamper the build-up of genetic divergence. Despite this, divergence appears to occur occasionally at surprisingly small scales. The Galápagos archipelago provides an ideal opportunity to examine the evolutionary processes of local divergence in an isolated marine environment. Galápagos sea lions (Zalophus wollebaeki) are top predators in this unique setting and have an essentially unlimited dispersal capacity across the entire species range. In theory, this should oppose any genetic differentiation. 相似文献187.
The natural abundance of 15N in plant biomass has been used to infer how N dynamics change with elevated atmospheric CO2 and changing water availability. However, it remains unclear if atmospheric CO2 effects on plant biomass 15N are driven by CO2-induced changes in soil moisture. We tested whether 15N abundance (expressed as δ15N) in plant biomass would increase with increasing soil moisture content at two atmospheric CO2 levels. In a greenhouse experiment we grew sunflower (Helianthus annuus) at ambient and elevated CO2 (760 ppm) with three soil moisture levels maintained at 45, 65, and 85% of field capacity, thereby eliminating potential
CO2-induced soil moisture effects. The δ15N value of total plant biomass increased significantly with increased soil moisture content at both CO2 levels, possibly due to increased uptake of 15N-rich organic N. Although not adequately replicated, plant biomass δ15N was lower under elevated than under ambient CO2 after adjusting for plant N uptake effects. Thus, increases in soil moisture can increase plant biomass δ15N, while elevated CO2 can decrease plant biomass δ15N other than by modifying soil moisture. 相似文献
188.
P F Leadlay J Staunton M Oliynyk C Bisang J Cortés E Frost Z A Hughes-Thomas M A Jones S G Kendrew J B Lester P F Long H AI McArthur E L McCormick Z Oliynyk C BW Stark C J Wilkinson 《Journal of industrial microbiology & biotechnology》2001,27(6):360-367
The biosynthesis of complex reduced polyketides is catalysed in actinomycetes by large multifunctional enzymes, the modular
Type I polyketide synthases (PKSs). Most of our current knowledge of such systems stems from the study of a restricted number
of macrolide-synthesising enzymes. The sequencing of the genes for the biosynthesis of monensin A, a typical polyether ionophore
polyketide, provided the first genetic evidence for the mechanism of oxidative cyclisation through which polyethers such as
monensin are formed from the uncyclised products of the PKS. Two intriguing genes associated with the monensin PKS cluster
code for proteins, which show strong homology with enzymes that trigger double bond migrations in steroid biosynthesis by
generation of an extended enolate of an unsaturated ketone residue. A similar mechanism operating at the stage of an enoyl
ester intermediate during chain extension on a PKS could allow isomerisation of an E double bond to the Z isomer. This process, together with epoxidations and cyclisations, form the basis of a revised proposal for monensin formation.
The monensin PKS has also provided fresh insight into general features of catalysis by modular PKSs, in particular into the
mechanism of chain initiation. Journal of Industrial Microbiology & Biotechnology (2001) 27, 360–367.
Received 18 March 2001/ Accepted in revised form 09 July 2001 相似文献
189.
190.
Elevated atmospheric CO2 stimulates aboveground biomass in a fire-regenerated scrub-oak ecosystem 总被引:2,自引:0,他引:2
Paul Dijkstra Graham Hymus Debra Colavito David A. Vieglais† Christina M. Cundari‡ David P. Johnson Bruce A. Hungate§ C. ROSS Hinkle‡ Bert G. Drake 《Global Change Biology》2002,8(1):90-103
The effect of elevated atmospheric CO2 concentration (Ca) on the aboveground biomass of three oak species, Quercus myrtifolia, Q. geminata, and Q. chapmanii, was estimated nondestructively using allometric relationships between stem diameter and aboveground biomass after four years of experimental treatment in a naturally fire‐regenerated scrub‐oak ecosystem. After burning a stand of scrub‐oak vegetation, re‐growing plants were exposed to either current ambient (379 µL L?1 CO2) or elevated (704 µL L?1 CO2) Ca in 16 open‐top chambers over a four‐year period, and measurements of stem diameter were carried out annually on all oak shoots within each chamber. Elevated Ca significantly increased aboveground biomass, expressed either per unit ground area or per shoot; elevated Ca had no effect on shoot density. The relative effect of elevated Ca on aboveground biomass increased each year of the study from 44% (May 96–Jan 97), to 55% (Jan 97–Jan 98), 66% (Jan 98–Jan 99), and 75% (Jan 99–Jan 00). The effect of elevated Ca was species specific: elevated Ca significantly increased aboveground biomass of the dominant species, Q. myrtifolia, and tended to increase aboveground biomass of Q. chapmanii, but had no effect on aboveground biomass of the subdominant, Q. geminata. These results show that rising atmospheric CO2 has the potential to stimulate aboveground biomass production in ecosystems dominated by woody species, and that species‐specific growth responses could, in the long term, alter the composition of the scrub‐oak community. 相似文献