Augmentation of Nitrite-reducing Capacity of Ruminal Bacteria

1)原生动物对硝酸盐和亚硝酸盐还原的影响原生动物与细菌共存时硝酸盐还原率高于单独培养细菌时。原生动物对亚硝酸盐的还原作用大于对硝酸盐的还原作用，从而减少了亚硝酸盐的积累。原生动物对硝酸盐和亚硝酸盐还原的刺激主要是由于原生动物产生H2和乳酸（电子供体）。2)能量底物对反刍硒单胞菌硝酸还原酶和硝酸还原酶的影响硝酸还原速率与细胞内硝酸还原酶（NaR）的量平行。NaR的数量与生长速率呈负相关。硝酸还原率（NaR的量）与细胞内ATP水平和NADH / NAD^+比值呈负相关。因此，硝酸还原酶的合成可能受到能量和电子供应充足的调节。硝酸促进了NaR的合成。3)竞争聚合酶链反应（pcr）法测定山羊瘤胃中硝酸盐还原菌数量反刍S.瘤胃细胞数量远大于细小细孔菌和琥珀酸Wollinella。然而，后两种细菌的数量通过喂食高硝酸盐饮食而增加。4)硝酸盐和亚硝酸盐还原对甲烷生成抑制的影响上述三种细菌通过电子传递磷酸化结合硝酸盐和/或亚硝酸盐还原获得能量，并且比其他瘤胃细菌更耐受亚硝酸盐毒性。因此，高硝酸盐饲料可能有利于这些细菌在瘤胃中的生长。由于这三种细菌的存在，甲烷产量显著降低。产甲烷细菌对亚硝酸盐比其他细菌更敏感，这可能是抑制甲烷生成的另一个原因。

1) Effect of protozoa on nitrate and nitrite reductionNitrate reduction rate was higher when protozoa coexisted with bacteria than when only bacteria were grown. The effect of protozoa was greater on nitrite reduction than on nitrate reduction, which resulted in decreased nitrite accumulation. Stimulation of nitrate and nitrite reduction by protozoa was shown to be mainly due to the production of H2 and lactate (electron donors) by protozoa.2) Effects of energy substrates on nitrate reduction and nitrate reductase in Selenomonas ruminantiumNitrate reduction rate was parallel to the amount of nitrate reductase (NaR) in cells. The amount of NaR was inversely related to growth rate. Nitrate reduction rate (the amount of NaR) was inversely related to the level of intracellular ATP and the ratio of NADH to NAD^+. Therefore, the synthesis of nitrate reductase may be regulated in response to the sufficiency of energy and electron supply. NaR synthesis was suggested to be enhanced by nitrate.3) Numbers of nitrate-reducing bacteria in the rumen as estimated by competitive PCRThe cell number of S. ruminantium in the rumen of goats was much larger than Veillonella parvula and Wollinella succinogenes. However, the numbers of the latter two bacteria were increased by feeding a high-nitrate diet.4) Effect of nitrate and nitrite reduction on the suppression of methanogenesisThe above three bacteria were found to acquire energy by electron transport phosphorylation coupled with nitrate and/or nitrite reduction, and are more tolerant to nitrite toxicity than other ruminal bacteria. Therefore, high-nitrate diets may favors the growth of these bacteria in the rumen. Methane production was markedly reduced by the presence of the three bacteria. Methanogenic bacteria were shown to be more sensitive to nitrite than other bacteria, which may additionally suppress methanoaenesis.