Characterization of cellulolytic symbionts among the core gut microbiota in giant panda (Ailuropoda melanoleuca)

Despite being a member of the genus Carnivora, giant pandas consume a plant-based diet, bamboo being their major dietary component. Due to lack of putative enzymatic genes in their genome, the microbial contributions to cellulose metabolism in giant pandas have been questioned for a few decades. To determine the effects of dietary selection and herbivorous behavior on gastrointestinal microbiota in giant panda, we performed both massive parallel pyrosequencing of 16s rRNA genes and extensive cultural studies using the fresh fecal materials of giant pandas. The microbial profile was primarily predominated by either Proteobacteria or Firmicutes and diversity abundance reflects on the individual due to the individual animal’s selectiveness on bamboos species they ingest. Numbers of observed species and diversity estimations indicated that giant pandas have preserved a higher bacterial diversity like other herbivorous animals. We also further analyzed a core gut bacterial community of the giant panda, from which we demonstrated putative cellulose-metabolizing symbionts. Therefore, the cellulose metablosim in giant panda’s gastrointestinal tract (GIT) may originate from symbiontic interactions among cellulolytic microbes. Using available cultural methods, we isolated at least seven different cellulolytic genera. Their roles in the digestive physiology of giant panda deserve to further investigation. Moreover, the significant association of core gut mcirobiota of captive giant pandas with human microbiome may be explained by a shift in bacterial flora ecology due to the use of human care in hand rearing captive born giant pandas.

尽管大熊猫属于食肉目（Carnivora），但其日粮以植物性食物为主，竹子为其核心食物来源。由于基因组中缺乏推定的纤维素酶编码基因，数十年来，肠道微生物对大熊猫纤维素代谢的贡献一直备受学界质疑。为探究饮食选择与植食性行为对大熊猫肠道菌群的影响，本研究采集大熊猫新鲜粪便样本，同时开展了16S rRNA基因大规模平行焦磷酸测序（massive parallel pyrosequencing）与系统性培养组学研究。结果显示，大熊猫肠道微生物群落结构主要以变形菌门（Proteobacteria）或厚壁菌门（Firmicutes）为优势类群；菌群多样性与丰度因个体对采食竹种的选择性存在显著差异。观测物种数与多样性评估结果表明，大熊猫与其他植食性动物一样，保有较高的细菌群落多样性。本研究还进一步解析了大熊猫核心肠道菌群，并从中鉴定出推定的纤维素分解共生菌。因此，大熊猫胃肠道（gastrointestinal tract, GIT）内的纤维素代谢可能源于纤维素分解微生物间的共生相互作用。本研究通过现有培养方法，分离得到至少7个不同的纤维素分解菌属，这些菌属在大熊猫消化生理中的作用仍有待深入探究。此外，圈养大熊猫的核心肠道菌群与人类菌群存在显著关联，该现象可归因于人工护理圈养新生大熊猫过程中引发的细菌群落生态学改变。