科研人員發(fā)現(xiàn)了幫助大熊貓以竹子為食茁壯成長(zhǎng)的消化道微生物,。
擁有類(lèi)似于食肉動(dòng)物的胃腸道的大熊貓的飲食習(xí)慣長(zhǎng)久以來(lái)讓科研人員感到困惑。
大熊貓是一種雜食性的熊,，每天消耗至多12公斤竹子,，它缺乏幫助草食動(dòng)物消化纖維素和半纖維素（它們是纖維性植物飲食的主要成分）的酶。
Fuwen Wei及其同事使用了基因測(cè)序技術(shù)來(lái)發(fā)現(xiàn)生活在大熊貓消化道中的微生物,，希望發(fā)現(xiàn)消化纖維素的共生體——而此前的嘗試沒(méi)能發(fā)現(xiàn)它們,。
這組作者分析了5000多個(gè)核糖體RNA序列，以此作為見(jiàn)于野生和捕獲的大熊貓的糞樣本中發(fā)現(xiàn)的微生物的遺傳條碼,，然后與那些見(jiàn)于食草動(dòng)物的序列進(jìn)行了比較,。
這組作者報(bào)告說(shuō)，7種在分類(lèi)學(xué)上與梭菌有密切關(guān)系的細(xì)菌是熊貓糞獨(dú)有的—梭菌已知能消化纖維素,。
此外,，這組作者還發(fā)現(xiàn)了消化纖維素和半纖維素的酶的推定的基因序列。
這組作者這說(shuō),，再加上諸如偽拇指,、強(qiáng)壯的牙齒、咀嚼肌和豐富的消化道黏液等其他適應(yīng),，消化纖維素的腸道細(xì)菌可能有助于維持熊貓的在肉食動(dòng)物中不尋常的飲食習(xí)慣,。
doi:10.1073/pnas.1017956108
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Evidence of cellulose metabolism by the giant panda gut microbiome
Lifeng Zhu, Qi Wu, Jiayin Dai, Shanning Zhang, and Fuwen Wei
The giant panda genome codes for all necessary enzymes associated with a carnivorous digestive system but lacks genes for enzymes needed to digest cellulose, the principal component of their bamboo diet. It has been posited that this iconic species must therefore possess microbial symbionts capable of metabolizing cellulose, but these symbionts have remained undetected. Here we examined 5,522 prokaryotic ribosomal RNA gene sequences in wild and captive giant panda fecal samples. We found lower species richness of the panda microbiome than of mammalian microbiomes for herbivores and nonherbivorous carnivores. We detected 13 operational taxonomic units closely related to Clostridium groups I and XIVa, both of which contain taxa known to digest cellulose. Seven of these 13 operational taxonomic units were unique to pandas compared with other mammals. Metagenomic analysis using ∼37-Mbp contig sequences from gut microbes recovered putative genes coding two cellulose-digesting enzymes and one hemicellulose-digesting enzyme, cellulase, β-glucosidase, and xylan 1,4-β-xylosidase, in Clostridium group I. Comparing glycoside hydrolase profiles of pandas with those of herbivores and omnivores, we found a moderate abundance of oligosaccharide-degrading enzymes for pandas (36%), close to that for humans (37%), and the lowest abundance of cellulases and endohemicellulases (2%), which may reflect low digestibility of cellulose and hemicellulose in the panda's unique bamboo diet. The presence of putative cellulose-digesting microbes, in combination with adaptations related to feeding, physiology, and morphology, show that giant pandas have evolved a number of traits to overcome the anatomical and physiological challenge of digesting a diet high in fibrous matter.
