Bacterial cultures enriched from sheep rumen fluid have demonstrated the ability to detoxify pyrrolizidine alkaloids (seneciphylline and jacobine) in tansy ragwort (Senecio jacobaea). The microbes are difficult to isolate using classical anaerobic techniques, therefore, microbes from two different enrichment cultures demonstrating similar degradation activity were identified using their 16S ribosomal RNA genes. Gene sequences from a rich medium enrichment were matched to Clostridium bifermentans, Prevotella ruminicola, Escherichia coif, and from a minimal medium enrichment to, C. clostridiiforme, C. aminophilum, Streptococcus bovis, and Butyrivibrio fibrosolvens. There were no identical organisms between the two libraries, but the common genus was Clostridium. / Graduation date: 1998

Ruan, Jianqing. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 162-175). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

The pyrrolizidine alkaloids (PAs) and ergot alkaloids are known natural toxicants found in livestock forage. These alkaloids contribute to large economic losses in livestock throughout the world. An understanding of the mechanisms of toxicity and development of better diagnostic tools for better management practices was investigated. Variability exists in the toxicity of PAs in ruminants where cattle are more susceptible and sheep are more resistant. The mechanism of PA resistance in sheep has been attributed to hepatic metabolism or rumen microbial degradation of PAs to non-toxic moieties. The hepatic metabolism of the PA senecionine was investigated in cattle and sheep liver microsomes. The level of a toxic pyrrole metabolite 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine pyrrole (DHP) formed in cattle and sheep were similar. However, the level of a non-toxic N-oxide metabolite was greater in sheep than in cattle. Cytochrome P450 and flavin monooxygenases (FMOs) responsible for PA oxidative metabolism were similar in both ruminant species. Therefore, hepatic metabolism of PAs is not solely responsible for resistance observed in sheep versus cattle. Ergot alkaloids present in endophyte-infected plants also cause toxicity in livestock. HPLC is the typical method used to quantify ergot alkaloid content; however, it is costly and time-consuming. An enzyme-linked immunosorbent assay (ELISA) developed with lysergol as the hapten was evaluated to ascertain its feasibility as an analytical tool for the ergot alkaloids found in forage plants. The ELISA detected the presence of lysergic acid but was not a reliable assay for the ergopeptine alkaloids such as ergovaline. The genetic divergence in mice previously selected into ergot alkaloid susceptible and resistant lines was studied after ten generations of relaxed selection. Physiologically no difference was seen between the susceptible and resistant line for average daily weight gain. However, hepatic metabolism of the ergot alkaloid ergotamine showed differences between genders and between animals on diets containing no ergot alkaloids or a high concentration of ergot alkaloids. Four major biotransformation products were identified as hydroxylated ergotamine isomers based on mass spectroscopic analysis. / Graduation date: 2003

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