Sulfate and nitrate reduction, and methanogenesis in mammalian digestive tract

以绵羊瘤胃和猪盲肠混合菌群为研究对象，研究了专一性产甲烷抑制剂BES对碳水化合物发酵产氢的影响。BES对瘤胃微生物的影响是明显的，BES积累的氢是猪盲肠微生物的100 - 2000倍，而相同处理的猪盲肠微生物积累的氢是5 - 10倍。结果表明，瘤胃中绝大部分氢气是通过产甲烷作用进行处理的。测定了绵羊瘤胃和猪盲肠中产甲烷菌和硫酸盐还原菌的数量。瘤胃中的优势氢营养菌为产甲烷菌，而猪盲肠中的优势氢营养菌为硫酸盐还原菌。这种情况在瘤胃中尤为明显，因为在大多数厌氧环境中，硫酸盐还原菌是主要的氢营养菌。通过使用HPLC的离子色谱法测量了羊睾丸中的游离硫酸盐水平。 ...更多信息 瘤胃内的N-P浓度在饲喂后1h高达1 mM，饲喂后最高，饲喂后4 h逐渐下降至零。在猪盲肠中的最高水平高达5 mM。水平始终高于瘤胃液中观察到的水平。低硫酸盐水平似乎是造成瘤胃中硫酸盐还原活性低的原因。使用瘤胃液进行体外实验，以了解需要何种水平的硫酸盐来增强硫酸盐还原。当游离硫酸盐浓度低于10 mM时，98%的氢气通过产甲烷作用处理，当游离硫酸盐浓度为10 mM时，硫酸盐还原作用增强，产甲烷作用减弱。然而，90%的氢仍然通过产甲烷处理，甚至更高的硫酸盐水平（20 mM）。通过动物体内试验研究了硫酸盐对瘤胃内甲烷生成和硫酸盐还原的影响。瘤胃中的游离硫酸盐水平因硫酸钠剂量而增加3至4倍。随着游离硫酸盐浓度的增加，利用乳酸盐的硫酸盐还原菌数量增加，硫酸盐还原活性增强。然而，利用H2的硫酸盐还原剂没有增加。投加硫酸钠后，产甲烷菌数量呈下降趋势，但各试验期间差异不一致。硫酸盐还原菌对硫酸盐水平增加缺乏明确的反应可能是由于硫酸盐增加不足，但仍然表明硫酸盐还原菌不能胜过瘤胃中的产甲烷菌。瘤胃中产甲烷菌和产氢菌之间的关系可能是如此密切，以至于其生态位不太可能被硫酸盐还原菌所取代。甲烷菌与产氢微生物如原生动物、壶菌、纤维素分解菌之间的关系有待进一步研究。少

Effect of specific methanogenic inhibitor (BES,2-bromo ethanesulphonate) on hydrogen accumulation from carbohydrate fermentation was investigated with ovine ruminal and porcine caecal mixed microorganisms. Effect of BES was evident with ruminal microorganisms, 100 to 2000 times more hydrogen was accumulated by BES,while 5 to 10 times more hydrogen was accumulated by the same treatment with porcine caecal microorganisms. It was suggested that most of hydrogen is disposed through methanogenesis in the rumen. The numbers of methanogenic and sulfate reducing bacteria were estimated in ovine rumen and porcine caecum. The predominant hydrogenotrophic bacterium was the methanogen in the rumen, while it was sulfate reducers in the porcine caecum. This situation was particular in the rumen, because sulfate reducers are predominant hydrogenotrophs in the most of anaerobic environment. Free sulfate levels in the digesta were measured by ion chromatography using HPLC.Free sulfate levels in the ovi … More ne rumen was as high as 1mM at 1h after feeding, the highest levels after feeding, the levels were gradually declined to zero 4h after feeding. The maximal level was as high as 5mM in the porcine caecum. The levels were constantly higher than those observed in ruminal fluid. The low sulfate levels appear to be responsible for low activity of sulfate reduction in the rumen. In vitro experiments were conducted using ruminal fluid in order to know what level of sulfate is required to enhance sulfate reduction. 98% of hydrogen was disposed through methanogenesis with free sulfate levels below 10mM.Sulfate reduction was enhanced and methanogenesis was reduced at 10mM of free sulfate. However 90% of hydrogen still disposed through methanogenesis even higher sulfate levels (20mM). In vivo experiment was conducted to know the effect of sulfate on methanogenesis and sulfate reduction in the rumen. Free sulfate levels were 3 to 4 times increased by the sodium sulfate dose in the rumen. The numbers of lactate-utilizing sulfate reducers and sulfate reducing activity of digesta increased according to the augmentation of free sulfate. However, H2-utilizing sulfate reducers did not increase. The numbers of methanogens tended to be decreased after sodium sulfate dose, the difference were not consistent between the experimental periods. Lack of clear response of sulfate reducers to increased sulfate levels may be due to the insufficient sulfate augmentation, but it is still suggested that sulfate reducers could not outcompete methanogens in the rumen. The relation between methanogens and H2-producing organisms in the rumen may be so close that the niche is unlikely to be replaced by sulfate reducers. Further studies are required to clarify the relation between methanogens and H2-producing organisms, such as protozoa, chytridiomycete fungi and cellulolytic bacteria. Less