Rumen archaea play an important role in scavenging ruminal hydrogen (H₂) and thus facilitate rumen fermentation. They require optimum temperature and osmolality for their growth and metabolism; however, a number of external factors may put archaea under heat and osmotic stress. Betaine is an osmolyte, molecular chaperone, and antioxidant; therefore, it bears potential to combat against these stressors. In this in vitro study, three betaine levels, namely, 0 (control), 51 (low), and 286 (high) ppm, were used. Each of these was subjected to two temperatures (39.5 and 42°C) and two osmolality conditions (295 and 420 mOsmol kg^-1) with per treatment. Sequencing analyses of the solid phase (which use solid materials containing primarily fibrous materials of low-density feed particles) and the liquid phase (rumen fermenter liquid) using 16S rRNA revealed that more than 99.8% of the ruminal archaea in fermenters belong to the phylum Euryarchaeota. At the genus level, Methanobrevibacter was the most prevalent in both phases, and Methanosaeta was only detected in the liquid phase. The genera Methanobrevibacter and Methanobacterium both showed a positive correlation with methane (CH₄) formation in the liquid and solid phases, respectively (). Heat stress increased the relative abundance of genus Methanimicrococcus at the expense of candidate archaeal genus Vadin CA11 (). In the solid phase, osmotic stress significantly reduced the Shannon and Simpson indices of diversity, and relative abundance was higher for Methanobrevibacter at the expense of Methanimicrococcus. In the liquid phase, osmotic stress increased not only the abundance-based coverage estimator (ACE) and singles parameters of diversity but also the relative abundances of Methanosphaera and Methanobacterium. The overall decrease in all gas parameters and estimated metabolic hydrogen ([2H]) utilization was observed during osmotic stress conditions (). Betaine enhanced the diversity of solid phase archaea as indicated by the increase in ACE and singles during heat stress, and only a high dose improved all diversity parameters in the liquid phase during osmotic stress (). Thus, betaine alleviates the effects of heat stress and osmotic stress on the archaea community.

中文翻译：

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甜菜碱在体外热和渗透压力条件下调节瘤胃古菌群落和功能

瘤胃古菌在清除瘤胃氢（H ₂）方面发挥重要作用，从而促进瘤胃发酵。它们的生长和代谢需要最佳温度和渗透压；然而，许多外部因素可能会使古细菌面临高温和渗透压力。甜菜碱是一种渗透剂、分子伴侣和抗氧化剂；因此，它具有对抗这些压力源的潜力。在这项体外研究中，使用了三种甜菜碱水平，即 0（对照）、51（低）和 286（高）ppm。其中每一个都经受两个温度（39.5 和 42°C）和两个渗透压条件（295 和 420 mOsmol kg ^-1），其中每次治疗。固相（使用主要含有低密度饲料颗粒的纤维材料的固体材料）和液相（瘤胃发酵液）使用 16S rRNA 的测序分析表明，发酵罐中超过 99.8% 的瘤胃古细菌属于该门泛古菌。在属水平上，Methanobrevibacter在两相中最为普遍，而Methanosaeta仅在液相中检测到。Methanobrevibacter和Methanobacterium属分别与液相和固相中甲烷 (CH ₄ ) 的形成呈正相关（）。热应激以牺牲候选古菌 Vadin CA11 为代价增加了Methanimicrococcus属的相对丰度。）。在固相中，渗透胁迫显著降低多样性的香农和Simpson指数，和相对丰度较高为甲烷短为代价Methanimicrococcus。在液相中，渗透压力不仅增加了基于丰度的覆盖度估计值 (ACE) 和多样性的单项参数，而且还增加了Methanosphaera和Methanobacterium的相对丰度。在渗透胁迫条件下，观察到所有气体参数和估计的代谢氢 ([2H]) 利用率总体下降（）。甜菜碱增强了固相古细菌的多样性，如热应激期间 ACE 和单核菌的增加所示，并且只有高剂量才能改善渗透应激期间液相中的所有多样性参数。）。因此，甜菜碱减轻了热应激和渗透应激对古细菌群落的影响。