Pitta Dipti, Indugu Nagaraju, Narayan Kapil, Hennessy Meagan
Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square 19348.
Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square 19348.
J Dairy Sci. 2022 Oct;105(10):8569-8585. doi: 10.3168/jds.2021-21466. Epub 2022 Mar 26.
Ruminants are one of the largest sources of global CH emissions. This enteric CH is exclusively produced by methanogenic archaea as a natural product during microbial fermentation in the reticulorumen. As CH formation leads to a gross energy loss for the ruminant host and is also an environmental issue, several CH mitigation approaches have been investigated, but results have been inconsistent, which may be partially attributed to a lack of understanding of the mechanistic basis of methanogenesis and the effect of inhibitors on individual methanogenic lineages and other fermenting microbes in the rumen. Methanogenic archaea are obligatory anaerobes that can reduce CO, methanol, or methylamines or cleave acetate to form CH. Although methanogens work toward a common goal of generating energy through the formation of CH, individual methanogenic lineages differ in their physiological and metabolic capabilities, which can differentially affect H transactions and CH formation. Using advanced omic approaches, recent research has revealed that less abundant methanol-utilizing Methanosphaera and methylamine- and methanol-utilizing Methanomassiliicoccales lineages are positively correlated with CH emissions and may have a greater share in overall CH production compared with more abundant CO-reducing methanogens than previously thought. These data imply that the diversity as well as the abundance of methanogens is important in CH formation, and that this diversity is influenced by H availability and interactions within and between H-producing microbes in the rumen. These complex interactions between microbes and H are further influenced by variations in dietary, host, and environmental conditions. This review discusses critical knowledge gaps underlying methanogen diversity and its link to CH formation, formation of specific bacteria-archaeal cohorts, and how H production and utilization are regulated between these cohorts during normal and inhibited methanogenesis. Addressing these knowledge gaps has the potential to lead to the development of novel strategies or to complement existing strategies to effectively reduce CH formation while also improving productivity in dairy cows.
反刍动物是全球甲烷排放的最大来源之一。这种肠道甲烷是由产甲烷古菌在瘤胃微生物发酵过程中作为天然产物专门产生的。由于甲烷的形成会导致反刍动物宿主的总能量损失，并且也是一个环境问题，因此已经研究了几种甲烷减排方法，但结果并不一致，这可能部分归因于对甲烷生成的机制基础以及抑制剂对瘤胃中单个产甲烷谱系和其他发酵微生物的影响缺乏了解。产甲烷古菌是专性厌氧菌，能够还原二氧化碳、甲醇或甲胺，或者裂解乙酸盐以形成甲烷。尽管产甲烷菌都致力于通过甲烷形成来产生能量这一共同目标，但单个产甲烷谱系在生理和代谢能力上存在差异，这可能会对氢交换和甲烷形成产生不同影响。利用先进的组学方法，最近的研究表明，丰度较低的利用甲醇的甲烷球形菌以及利用甲胺和甲醇的甲烷鬃菌谱系与甲烷排放呈正相关，并且与丰度较高的还原二氧化碳产甲烷菌相比，它们在总甲烷产生中所占份额可能比以前认为的更大。这些数据表明，产甲烷菌的多样性以及丰度在甲烷形成中很重要，并且这种多样性受到瘤胃中氢的可用性以及产氢微生物内部和之间相互作用的影响。微生物与氢之间的这些复杂相互作用还受到饮食、宿主和环境条件变化的进一步影响。本综述讨论了产甲烷菌多样性及其与甲烷形成、特定细菌 - 古菌群落形成之间联系的关键知识空白，以及在正常和抑制甲烷生成过程中这些群落之间氢的产生和利用是如何受到调节的。填补这些知识空白有可能导致开发新的策略或补充现有策略，以有效减少甲烷形成，同时提高奶牛的生产力。
