Yang Chengjian, Rooke John A, Cabeza Irene, Wallace Robert J
Buffalo Research Institute, Chinese Academy of Agricultural Sciences Nanning, China.
Scotland's Rural College Edinburgh, UK.
Front Microbiol. 2016 Feb 12;7:132. doi: 10.3389/fmicb.2016.00132. eCollection 2016.
Ruminal methane production is among the main targets for greenhouse gas (GHG) mitigation for the animal agriculture industry. Many compounds have been evaluated for their efficacy to suppress enteric methane production by ruminal microorganisms. Of these, nitrate as an alternative hydrogen sink has been among the most promising, but it suffers from variability in efficacy for reasons that are not understood. The accumulation of nitrite, which is poisonous when absorbed into the animal's circulation, is also variable and poorly understood. This review identifies large gaps in our knowledge of rumen microbial ecology that handicap the further development and safety of nitrate as a dietary additive. Three main bacterial species have been associated historically with ruminal nitrate reduction, namely Wolinella succinogenes, Veillonella parvula, and Selenomonas ruminantium, but others almost certainly exist in the largely uncultivated ruminal microbiota. Indications are strong that ciliate protozoa can reduce nitrate, but the significance of their role relative to bacteria is not known. The metabolic fate of the reduced nitrate has not been studied in detail. It is important to be sure that nitrate metabolism and efforts to enhance rates of nitrite reduction do not lead to the evolution of the much more potent GHG, nitrous oxide. The relative importance of direct inhibition of archaeal methanogenic enzymes by nitrite or the efficiency of capture of hydrogen by nitrate reduction in lowering methane production is also not known, nor are nitrite effects on other members of the microbiota. How effective would combining mitigation methods be, based on our understanding of the effects of nitrate and nitrite on the microbiome? Answering these fundamental microbiological questions is essential in assessing the potential of dietary nitrate to limit methane emissions from ruminant livestock.
瘤胃甲烷生成是畜牧业温室气体减排的主要目标之一。许多化合物已被评估其抑制瘤胃微生物产生肠道甲烷的功效。其中，硝酸盐作为替代氢汇一直是最有前景的，但由于尚不清楚的原因，其功效存在差异。亚硝酸盐的积累在被动物循环系统吸收时是有毒的，其积累情况也各不相同且了解甚少。本综述指出，我们对瘤胃微生物生态学的认识存在很大差距，这阻碍了硝酸盐作为饲料添加剂的进一步发展和安全性。历史上，三种主要细菌物种与瘤胃硝酸盐还原有关，即琥珀酸沃林氏菌、小韦荣氏球菌和反刍月形单胞菌，但在很大程度上未培养的瘤胃微生物群中几乎肯定还存在其他细菌。有充分迹象表明纤毛虫原生动物可以还原硝酸盐，但其相对于细菌的作用意义尚不清楚。还原硝酸盐的代谢命运尚未得到详细研究。必须确保硝酸盐代谢以及提高亚硝酸盐还原率的努力不会导致产生更强效的温室气体一氧化二氮。亚硝酸盐对古菌产甲烷酶的直接抑制作用或硝酸盐还原捕获氢在降低甲烷生成方面的效率的相对重要性也不清楚，亚硝酸盐对微生物群其他成员的影响也不清楚。根据我们对硝酸盐和亚硝酸盐对微生物组影响的理解，联合减排方法的效果如何？回答这些基本的微生物学问题对于评估饲料硝酸盐限制反刍家畜甲烷排放的潜力至关重要。
