Effects of pH and Concentrations of Linoleic and Linolenic Acids on Extent and Intermediates of Ruminal Biohydrogenation in Vitro

Three experiments were conducted by in vitro incubations in ruminal fluid to investigate the effects of pH and amounts of linoleic and linolenic acids on the extent of their biohydrogenation, the proportions of conjugated linoleic acid (CLA) and trans-C18:1 as intermediates, and the ratio trans-10:trans-11 intermediates. The effects of pH and amount of linoleic acid were investigated in kinetic studies, and effects of the amount of linolenic acid were studied with 6-h incubations. With identical initial amounts of linoleic acid, its disappearance declined when the mean pH during incubation was under 6.0 compared with a mean pH over 6.5, and when the amount of linolenic acid increased from 10 to 180 mg/160-ml flask, suggesting an inhibition of the isomerization step of the biohydrogenation. Low pH decreased the ratio of trans-10:trans-11 intermediates. With initial amounts of linoleic acid increasing from 100 to 300 mg, the percentage of linoleic acid disappearance declined, but the amount that disappeared increased, without modification of the trans-10:trans-11 ratio, suggesting a maximal capacity of isomerization rather than an inhibition. Moreover, increasing initial linoleic acid resulted in high amounts of trans-C18:1 and an increase of C18:0 that was a linear function of time, suggesting a maximal capacity for the second reduction step of biohydrogenation. High amounts of initial linolenic acid did not affect the amounts of CLA, trans-C18:1, or the ratio trans-10:trans-11. Based on these experiments, a ruminal pH near neutrality with high amount of dietary linoleic acid should modulate the reactions of biohydrogenation in a way that supports CLA and trans-11C18:1 in the rumen

Effects of live yeast on the fatty acid biohydrogenation by ruminal bacteria

Addition of live yeasts in high concentrate diets for ruminants has been shown to help maintaining the ruminal pH above 6, which could enhance the microbial biohydrogenation of unsaturated dietary fatty acids. Moreover, yeasts improve the growth of Megasphera elsdenii, a bacteria which favors the trans-10 pathway of biohydrogenation. So the objective of this study was to investigate the effects of live yeasts (Saccharomyces cerevisiae) on the biohydrogenation in the rumen of dairy cows receiving a high concentrate diet without added fat. Three ruminally fistulated lactating dairy cows were given three diets based on corn silage (control, control plus 0.5g/d or control plus 5.0g/d of Saccharomyces cerevisiae NCYC SC47), according to a Latin square design. Ruminal contents were sampled and liquid and solid phases were separated with a 0.25mm metal sieve. Fatty acids profiles were obtained by gas chromatography. The two doses of yeast resulted in similar effects. Live yeast significantly decreased myristic and stearic acids proportions, and significantly increased oleic and linoleic acids proportions by 16 and 32% in the liquid and the solid phases, respectively. No significant effect was observed for other biohydrogenation intermediates, but the cis9,trans11-C18:2 tended (P = 0.154) to increase with the addition of yeasts, whereas trans10-C18:1 numerically decreased (P = 0.225). These results suggested that live yeasts affect microbial activity, lowering the extent of biohydrogenation without shifting toward the trans-10 isomers pathway

In Vitro Versus in Situ Ruminal Biohydrogenation of Unsaturated Fatty Acids from a Raw or Extruded Mixture of Ground Canola Seed/Canola Meal

Raw or extruded blends of ground canola seeds and canola meal were used to compare in vitro and in situ lag times and rates of disappearance due to ruminal biohydrogenation of unsaturated fatty acids. The in situ study resulted in higher lag times for biohydrogenation for polyunsaturated fatty acids and lower rates of biohydrogenation of unsaturated fatty acids than the in vitro study, so the in situ biohydrogenation of polyunsaturated fatty acids was not complete at 24 h of incubation. With both methods, rates of biohydrogenation of polyunsaturated fatty acids were higher than for cis-9C18:1. Extrusion did not affect the rate of biohydrogenation of cis-9C18:1, but resulted in higher rates of biohydrogenation of polyunsaturated fatty acids with higher proportions of trans intermediates of biohydrogenation at 4 h of incubation in vitro and at 8 h of incubation in situ. These results suggest that extrusion affects the isomerization of polyunsaturated fatty acids, rather than the hydrogenation steps. In conclusion, in vitro and in situ methods can both show differences of ruminal metabolism of unsaturated fatty acids due to processing, but the methods provide very different estimates of the rates of disappearance due to biohydrogenation

HST's view of the youngest massive stars in the Magellanic Clouds

Accurate physical parameters of newborn massive stars are essential ingredients to shed light on their formation, which is still an unsolved problem. The rare class of compact H II regions in the Magellanic Clouds (MCs), termed ``high-excitation blobs'' (HEBs), presents a unique opportunity to acquire this information. These objects (~ 4" to 10", ~ 1 to 3 pc, in diameter) harbor the youngest massive stars of the OB association/molecular cloud complexes in the MCs accessible through high-resolution near-IR and optical techniques. We present a brief overview of the results obtained with HST mainly on two HEBs, one in the LMC (N159-5) and the other in the SMC (N81).Comment: 5 pages, to appear in the Proceedings of the 41st ESLAB Symposium "The Impact of HST on European Astronomy", 29 May to 1 June 2007, ESTEC, Noordwijk, Netherlands; eds. Guido De Marchi and Duccio Macchett

Two compact HII regions at the remote outskirts of the Magellanic Clouds

The H II regions LMC N191 and SMC N77 are among the outermost massive star-forming regions in the Magellanic Clouds. So far, few works have dealt with these objects despite their interesting characteristics. We aim at studying various physical properties of these objects regarding their morphology (in the optical and Spitzer IRAC wavelengths), ionized gas emission, nebular chemical abundances, exciting sources, stellar content, age, presence or absence of young stellar objects, etc. This study is based mainly on optical ESO NTT observations, both imaging and spectroscopy, coupled with other archive data, notably Spitzer images (IRAC 3.6, 4.5, 5.8, and 8.0 microns) and 2MASS observations. We show the presence of two compact H II regions, a low-excitation blob (LEB) named LMC N191A and a high-excitation blob (HEB) named SMC N77A, and study their properties and those of their exciting massive stars as far as spectral type and mass are concerned. We also analyze the environmental stellar populations and determine their evolutionary stages. Based on Spitzer IRAC data, we characterize the YSO candidates detected in the direction of these regions. Massive star formation is going on in these young regions with protostars of mass about 10 and 20 M_sun in the process of formation.Comment: 14 pages, 8 figures, 6 tables; Accepted for publication in A&A. arXiv admin note: substantial text overlap with arXiv:1102.125

In situ ruminal biohydrogenation of fatty acids from extruded soybeans: effects of dietary adaptation and of mixing with lecithin or wheat straw

Kinetics and intermediates of biohydrogenation of fatty acids were investigated in situ using extruded soybeans, a blend of extruded soybeans and lecithin (99:1), or a blend of extruded soybeans plus wheat straw (66:34). Two dry dairy cows received successively a diet with added palmitic acid and a diet with added extruded soybeans, and assays were completed after a 3-week adaptation to each diet. Adaptation of the cows to dietary polyunsaturated fatty acids suppressed the lag time before the beginning of biohydrogenation. Adaptation of cows, and mixing straw with soybeans, increased the rate of biohydrogenation of C18:2 and C18:3, resulting in less C18:2 and C18:3, and more trans C18:1 and C18:0 in the in situ bags. Lecithin did not affect the kinetics of biohydrogenation or the profile of fatty acids in the in situ bags. Differences in the rate of biohydrogenation, and profile of residual fatty acids in the bags were observed between the two cows. Even with a mixture of soybeans and straw in cows receiving dietary polyunsaturated fatty acids, biohydrogenation was slower and resulted in higher proportions of trans-C18:1 than expected from results of literature in vivo. Resultsshow that the biohydrogenation in situ is slow, highly dependent on experimental conditions, and that the use of several cows, adapted to the test fat source before the assay is initiated, is necessary in order to obtain a reliable estimate of kinetics parameters

The stellar environment of SMC N81

We present near infrared JHK imaging of the Small Magellanic Cloud compact H II region N81 using the ISAAC camera at the ESO Very Large Telescope (Antu). Our analysis of the stellar environment of this young massive star region reveals the presence of three new stellar populations in the surrounding field which are mainly composed of low mass stars. The main population is best fitted by evolutionary models for about 2 solar mass stars with an age of 1 Gyr. We argue that these populations are not physically associated with the H II region N81. Instead they are the result of a number of low mass star forming events through the depth of the SMC south of its Shapley's wing. The populations can rather easily be probed due to the low interstellar extinction in that direction.Comment: 11 pages, 5 figures, accepted for publication in A&

Resolving the compact HII regions in N160A with HST

Using high-resolution imaging with the Hubble Space Telescope, we study the Large Magellanic Cloud HII region N160A and uncover several striking features of this complex massive star-forming site. The two compact high excitation HII blobs (HEBs) A1 and A2 are for the first time resolved and their stellar content and morphology is revealed. A1, being of higher excitation, is powered by a single massive star whose strong wind has created a surrounding bubble. A2 harbors several exciting stars enshrouded inside large quantities of dust. The whole N160A nebula is energized by three star clusters for which we obtain photometry and study their color-magnitude diagram. The HII region is particularly dusty, with extinction values reaching an A_v~2.5 mag in the visible, and it is separated from the molecular cloud by an outstanding ionization front. A previously detected infrared young stellar object is also accurately located with respect to the HII region.Comment: 11 pages, 5 figures. Accepted for publication in Astronomy & Astrophysics. A version of the paper with higher quality images is available at http://wwwusr.obspm.fr/~heydari/projects/N16

Spectrum and Variability of Mrk501 as observed by the CAT Imaging Telescope

The CAT Imaging Telescope has observed the BL Lac object Markarian 501 between March and August 1997. We report here on the variability over this time including several large flares. We present also preliminary spectra for all these data, for the low emission state, and for the largest flare.Comment: 4 pages, 4 figures, Late

Observation of the Crab Nebula Gamma-Ray Emission Above 220 Gev by the Cat Cherenkov Imaging Telescope

The CAT imaging telescope, recently built on the site of the former solar plant Themis (French Pyrenees), observed gamma-rays from the Crab nebula from October 1996 to March 1997. This steady source, often considered as the standard candle of very-high-energy gamma-ray astronomy, is used as a test-beam to probe the performances of the new telescope, particularly its energy threshold (220 GeV at 20 degrees zenith angle) and the stability of its response. Due to the fine-grain camera, an accurate analysis of the longitudinal profiles of shower images is performed, yielding the source position in two dimensions for each individual shower.Comment: 5 pages, 3 figures, Tex, contribution to 25th ICRC Durba