1. Show details of how the ruminal fermentation products butyrate, propionate and acetate are used in adult ruminants. In each case name the tissue(s) in which the metabolic processes you describe occur(s) and give an assessment of the importance of these fatty acids in the metabolism of adult ruminants.

 
2. Fermentation patterns of a number of bacterial species in the reticulo-rumen vary according to co-culture with other organisms. Co-culture with methanogens is an important determinant in this regard. Describe how fermentation by a cellulose fermenter such as Ruminococcus flavifaciens can be modified by co-culture with methanogens, and further explain how these alterations affect the growth of propionate producers such as Selenomonas species which are unable to ferment cellulose. Explain also how feed conversion efficiency in the host ruminant is susceptible to alteration by these interrelations.

 
3. Lactate is an important fermentation product in the reticulo-rumen of normal adult ruminants. It is readily absorbed from the reticulo-rumen and is readily used by the host ruminant. Lactic acidosis is however a problem in adult ruminants given unrestricted access to readily fermentable grain products. This is due to overgrowth of other organisms by Lactobacilli under these conditions. Describe the pathway by which lactate is used in the liver of the host ruminant under normal conditions and describe also the pathway in Lactobacilli that generates lactic acid in large amounts under conditions of overgrowth by Lactobacilli as occurs as the result of grain engorgement.

 
4. The growth and fermentation products of ruminal bacteria that possess hydrogenases sensitive to the partial pressure of hydrogen are greatly influenced by co-culture with methanogens. Explain this statement giving biochemical detail where appropriate.

 
5. Propionate is a product of ruminal fermentation that has a special important function in the host animal. Describe the importance to the adult ruminant of having propionate available as a fermentation product and give a brief account of relevant biotransfromations to support your argument.

 
6. Describe the heterolactate pathway of glucose fermentation in Lactobacilli. In addition show how the butyrate and lactate produced as end products of this process in the reticulo-rumen may be used by the host ruminant.

 
7. A substantial proportion of butyrate absorbed from the reticulo-rumen may be converted into ketone bodies in the host rumen mucosal and liver cells. The ketone bodies themselves are subsequently oxidatively metabolized in peripheral tissues such as myocardium. Describe ketone body biosynthesis from butyrate and describe also the metabolic route by which ketone body carbon may be incorporated into tricarboxylic acid cycle intermediates in the cells of peripheral tissues.

 
8. Explain the way acetate and succinate production are coupled in the cellulose fermenter Fibrobacter succinogenes and explain the further fate of each of these two organic acid end products.

 
9. Explain why primary producers regard methanogenesis as a "bad thing" and explain also why it is, nevertheless, not a good idea to try to eliminate it completely in the reticulo-rumen environment.

 
10. Most microorganisms in the reticulo-rumen obtain their ATP by fermentation of hexose and/or pentose sugars. Some microorganisms however obtain their ATP by anaerobic respiration using a chemiosmotic mechanism where oxygen is not the ultimate electron acceptor. Explain, giving appropriate biochemical detail, the essential features of fermentation and anaerobic respiration and give details of one example of ATP production by each mechanism using a named microbial species found in the reticulo-rumen.

 
11. Syntrophic relationships are important among particular groups of microorganisms in the reticulo-rumen.  Describe what is meant by a syntrophic relationship and give details of one example showing the essential features you have identified.

 
12. Write a brief essay explaining the difference between symbiosis and syntrophy.

 
13. The phosphoroclastic cleavage pathway occurs in Enterobacteria which exhibit mixed acid fermentation.  Describe the sequence of metabolic conversions that constitute the phosphoroclastic pathway and explain the growth advantage this confers on these organisms.

 
14. A number of organisms in the reticulo-rumen use, as growth substrates, organic acids such as lactate or succinate, which are produced as waste products of the metabolism of other organisms.  Describe how these organic acids are used for this purpose.

 
15. Explain why homoacetogens are important microorganisms in the reticulo-rumen.