Hindgut dysbiotic microbiota contributes to the alterations of microbiota-derived metabolites during high ammonia exposure in growing pigs

The intestinal microbiome has been proven to affect host systematic metabolism and immune homeostasis. The current study aimed to investigate how aerial ammonia exposure influences the hindgut microbiota and its metabolites using pyrosequencing technologies in the pig model. Twelve growing pigs were randomly allocated to control or ammonia exposure (35 mg/m3) group respectively, and raised in two controlled chambers for 25d. A decreased trend of leptin (p = 0.0898) and reduced HDL-C (p = 0.0006) were found in serum after ammonia exposure. High ammonia exposure notably enhanced the alpha-diversity with higher sobs, shannon or ace index in cecum or colon and chao index in cecum (p < 0.05), indicating that high ammonia exposure increased the large intestinal microbiota species richness. Based on the bray-curtis distance and ANOSIM test, PCoA analysis demonstrated a distinct cluster clearly in cecum or colon after ammonia exposure (p < 0.01). In cecum, 17 genera were modified by ammonia exposure, followed by 6 genera in colon (FDR < 0.05). Ammonia exposure increased acetate and decreased isobutyrate or isovalerate in cecum or colon, respectively (p < 0.05). Cecal BA profiles showed that high ammonia exposure had a decreased trend of CA, HCA, LCA (p < 0.1), and decreased DCA, HDCA (p < 0.05), but increased GCDCA (p < 0.05). Contrary, an increased trend of HCA, LCA, HDCA (p < 0.1), a decreased trend of TDCA (p < 0.1) and decreased THDCA (p < 0.05) were observed in the serum BA profiles after ammonia exposure. Mantel test and correlation analysis revealed associations between microbiota-derived metabolites and ammonia exposure-responsive cecal bacteria. Collectively, our findings illustrated that high ammonia exposure induced the dysbiotic microbiota in hindgut, thereby affecting the production of microbiota-derived SCFAs and BAs, which play a pivotal role in the modulation of host systematic metabolism.

肠道微生物组业已被证实可影响宿主的系统性代谢与免疫稳态。本研究以猪为实验模型，采用焦磷酸测序（pyrosequencing）技术，旨在探究大气氨暴露对后肠菌群及其代谢产物的影响。将12头生长育肥猪随机分为对照组与氨暴露组（暴露浓度为35 mg/m³），于两个可控饲养舱中饲养25天。氨暴露后，受试猪血清中瘦素（leptin）呈下降趋势（p = 0.0898），高密度脂蛋白胆固醇（High-Density Lipoprotein Cholesterol, HDL-C）水平显著降低（p = 0.0006）。高浓度氨暴露可显著提升后肠菌群的α多样性：盲肠与结肠菌群的sobs、Shannon或Ace指数均显著升高，盲肠菌群的Chao指数亦显著升高（p < 0.05），表明高氨暴露可增加大肠菌群的物种丰富度。基于布雷-柯蒂斯距离（Bray-Curtis distance）与相似性分析检验（Analysis of Similarities, ANOSIM），主坐标分析（Principal Coordinates Analysis, PCoA）结果显示，氨暴露后猪盲肠与结肠菌群形成了清晰分离的聚类簇（p < 0.01）。在盲肠中，共有17个菌属的相对丰度在氨暴露后发生显著改变，结肠中则有6个菌属（错误发现率False Discovery Rate, FDR < 0.05）。氨暴露可分别使盲肠与结肠中的乙酸含量升高，异丁酸与异戊酸含量降低（p < 0.05）。盲肠胆汁酸（Bile Acids, BA）谱分析显示，高氨暴露使猪的胆酸（Cholic Acid, CA）、猪胆酸（Hyocholic Acid, HCA）、石胆酸（Lithocholic Acid, LCA）呈下降趋势（p < 0.1），脱氧胆酸（Deoxycholic Acid, DCA）、猪去氧胆酸（Hyodeoxycholic Acid, HDCA）水平显著降低（p < 0.05），但甘氨鹅脱氧胆酸（Glycochenodeoxycholic Acid, GCDCA）水平显著升高（p < 0.05）。与之相反，氨暴露后受试猪血清胆汁酸谱中，HCA、LCA、HDCA呈上升趋势（p < 0.1），牛磺脱氧胆酸（Taurodeoxycholic Acid, TDCA）呈下降趋势（p < 0.1），牛磺猪去氧胆酸（Taurohyodeoxycholic Acid, THDCA）水平显著降低（p < 0.05）。Mantel检验与相关性分析结果显示，菌群衍生代谢产物与氨暴露响应的盲肠菌群之间存在显著关联。综上，本研究结果表明，高浓度氨暴露可诱导后肠菌群失调，进而影响菌群衍生的短链脂肪酸（Short-Chain Fatty Acids, SCFAs）与胆汁酸的产生，而这些代谢产物在调控宿主系统性代谢过程中发挥关键作用。