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    Assessment of amino acid requirements for optimum fermentation of xylan by mixed micro-organisms from the sheep rumen
    (2005) Guliye, A.Y.; Atasoglu, C.; Wallace, R.J.
    A deletion approach was undertaken to identify which amino acids (AA) most limited the growth of mixed ruminal micro-organisms on xylan. Ruminal fluid was withdrawn from sheep receiving a mixed grass hay/concentrate diet and incubated for 24 h with oat spelts xylan in the presence or absence of a mixture of 20 AA or the same mixture with a single AA deleted. Gas and volatile fatty acid production were increased by the AA mixture in comparison with incubations in which ammonia was the only added nitrogen (N) source, and the deletion of each of the aromatic AA, tyrosine, phenylalanine and tryptophan, as well as leucine and methionine, led to decreases (P <0.05) in fermentation rate. The addition of aromatic AA as a mixture to ammonia-only fermentations increased (P <0.05) the fermentation rate but failed to replicate the benefits of the complete mixture of AA. Although the addition of all 20 AA increased (P <0.05) the microbial yield by up to 0.56, no single AA deletion had a significant (P >0.05) influence on microbial yield, and the aromatic AA mixture also did not increase the microbial yield on xylan over the yield with ammonia as sole N source. It was concluded that aromatic AA may be first-limiting for xylan fermentation, but they cannot replace the benefits of a complete mixture of 20 AA in stimulating xylan fermentation by ruminal micro-organisms. © 2005 British Society of Animal Science.
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    Mode of action of Chrysanthemum coronarium as a modulator of biohydrogenation of fatty acids in the rumen
    (Brill, 2023) Morales, E. Ramos; McKain, N.; Atasoglu, C.; Wood, T.A.; Wallace, R.J.
    [No abstract available]
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    Öğe
    Use of stable isotopes to measure de novo synthesis and turnover of amino acid-C and -N in mixed micro-organisms from the sheep rumen in vitro
    (2004) Atasoglu, C.; Guliye, A.Y.; Wallace, R.J.
    Protein synthesis and turnover in ruminal micro-organisms were assessed by stable-isotope methods in order to follow independently the fate of amino acid (AA)-C and -N in different AA. Rumen fluid taken from sheep receiving a grass hay-concentrate diet were strained and incubated in vitro with starch-cellobiose-xylose in the presence of NH3 and 5 g algal protein hydrolysate (APH)/l, in incubations where the labels were 15NH3, [15N]APH or [13C]APH. Total 15N incorporation was calculated from separate incubations with 15NH3 and [15N]APH, and net N synthesis from the increase in AA in protein-bound material. The large difference between total and net AA synthesis indicated that substantial turnover of microbial protein occurred, averaging 3.5 %/h. Soluble AA-N was incorporated on average more extensively than soluble AA-C (70 v. 50 % respectively, P=0.001); however, incorporation of individual AA varied. Ninety percent of phenylalanine-C was derived from the C-skeleton of soluble AA, whereas the incorporation of phenylalanine-N was 72 %. In contrast, only 15 % aspartate-C + asparagine-C was incorporated, while 45 % aspartate-N + asparagine-N was incorporated. Deconvolution analysis of mass spectra indicated substantial exchange of carboxyl groups in several AA before incorporation and a condensation of unidentified C2 and C4 intermediates during isoleucine metabolism. The present results demonstrate that differential labelling with stable isotopes is a way in which fluxes of AA synthesis and degradation, their biosynthetic routes, and separate fates of AA-C and -N can be determined in a mixed microbial population. © The Authors 2004.