Microbial Diversity and Evidence of Novel Homoacetogens in the Gut of Both Geriatric and Adult Giant Pandas (Ailuropoda melanoleuca)

Recent studies have described the bacterial community residing in the guts of giant pandas, together with the presence of lignocellulolytic enzymes. However, a more comprehensive understanding of the intestinal microbial composition and its functional capacity in giant pandas remains a major goal. Here, we conducted a comparison of bacterial, fungal and homoacetogenic microbial communities from fecal samples taken from two geriatric and two adult captive giant pandas. 16S rDNA amplicon pyrosequencing revealed that Firmicutes and Proteobacteria are the most abundant microbiota in both geriatric and adult giant pandas. However, members of phylum Actinobacteria found in adult giant pandas were absent in their geriatric counterparts. Similarly, ITS1 amplicon pyrosequencing identified developmental changes in the most abundant fungal classes from Sordariomycetes in adult pandas to Saccharomycetes in geriatric pandas. Geriatric pandas exhibited significantly higher abundance of a potential probiotic fungus (Candida tropicalis) as compared to adult pandas, indicating their importance in the normal digestive physiology of aged pandas. Our study also reported the presence of a lignocellulolytic white-rot fungus, Perenniporia medulla-panis, and the evidence of novel homoacetogens residing in the guts of giant pandas.既往研究已对大熊猫肠道内定植的细菌群落，以及木质纤维素降解酶（lignocellulolytic enzymes）的存在情况进行了阐述。然而，全面解析大熊猫肠道微生物组成及其功能潜能，仍是学界尚未实现的核心研究目标。本研究采集了2只老年圈养大熊猫与2只成年圈养大熊猫的粪便样本，对其中的细菌、真菌及同型产乙酸微生物群落（homoacetogenic microbial communities）开展了比较分析。16S rDNA扩增子焦磷酸测序（16S rDNA amplicon pyrosequencing）结果显示，厚壁菌门（Firmicutes）与变形菌门（Proteobacteria）是老年及成年大熊猫体内丰度最高的微生物类群。但成年大熊猫体内检出的放线菌门（Actinobacteria）类群，在老年个体中并未检出。与之类似，ITS1扩增子焦磷酸测序（ITS1 amplicon pyrosequencing）鉴定出优势真菌纲类群的演替变化：成年大熊猫的优势真菌纲为粪壳菌纲（Sordariomycetes），而老年大熊猫则为酵母纲（Saccharomycetes）。相较于成年大熊猫，老年大熊猫体内潜在益生菌真菌——热带假丝酵母（Candida tropicalis）的丰度显著更高，这表明该真菌在老年大熊猫的正常消化生理过程中发挥着重要作用。本研究同时报道了一种木质纤维素降解白腐真菌——髓层多年卧孔菌（Perenniporia medulla-panis）的存在，以及大熊猫肠道内定植新型同型产乙酸微生物的相关证据。