| Yaks (Bos grunniens) play a crucial role in the economy of the Qinghai-Tibetan Plateau by milk and meat for human living on and other by-products such as hides and fiber for tents. The high elevation areas, including Qinghai-Tibetan Plateau and Qilian mountains, are the only unimproved, no-polluted areas of the world and supplied only natural grasses for yaks. For these reasons, the rumen microbial of the yak is different from other ruminants such as cows and cattle. The dependence of the rumen microbial community structure on an animal's diet is a well-documented fact. But what's the specials and the differentials. This is one of the purports of our study.Recent progress in molecular microbial ecology has revealed that traditional culturing methods fail to represent the scope of microbial diversity in nature, since only a small proportion of viable microorganisms in a sample are recovered by culturing techniques. To estimated how many microbial specials there were and storage the genomic information of the gene, we constructed a cosmid library of microbial of rumen contents and analyzed the molecular microbial diversity by 16S rDNA sequence. At same time, a rapid and efficient method for extraction of DNA from the rumen contents which resulted in highly purified DNA with minimal shearing was developed.For protect and storage the genomic information of the yak rumen contents microorganisms' gene, a genomic cosmid library has been constructed. The genomic nuclear DNA was partially digested with Sau 3AI. The cosmid vector, pKC505, was digested with Hpa I and BamH I and dephosphorylated. The partially digested genomic DNA was purified with agar gel and the partials more than 20 kb were harvested. The purified fragments more than 20 kb were ligated to the vector and cloned into the E. coll LE392 according to the manufacturer's protocol. Approximately 6.7 X 104 individual cosmid clones were picked. The clones were digested by Pst I and electrophoresed with 1.2% agar gel. The insert fragments were checked and the insert size was 17-25 kb withaverage 21.5 kb.A culture-independent survey of the yak rumen content microbial diversity was conducted by sequence analysis of a universal clone library of genes coding for small-subunit rRNA (rDNA). Universal small-subunit-rRNA primers, 530f and 1492r, were used to amplify DNA extracted from the yak rumen content. The PCR procedure was 30 cycles and the products were cloned into pUCm-T and transformed into E. coli DH5a. The positive clones were picked up and checked by another PCR and sequenced. The universal clone library of genomic nuclear DNA from the Jinnan cattle (Bos turenns) were also constructed with same protocols. A total of 402 sequences, 184 from yak rumen content and the others from Jinnan cattle, containing partial 16S rDNA sequences (about 1.0 kb long), were partially sequenced and subjected to an on line similarity search. Twenty-eight sequences from the 184 clones of yak were closely related to the fibrolyses, including Butyrivlbrio fibrisolvens, Fibrobacter succinogenes, Ruminococcus albus, Ruminococcus flavefaciens, Clostridium xylanolyticum, Pseudobutyrivibrio ruminis, Pseudobutyrlvibrio xylanovorans and Uncultured fiber-attaching rumen bacteriums. But only 8 sequences from 218 clones of Jinnan cattle were related to this. With compared, twenty-five sequences from the 218 clones of Jinnan cattle were closely related to the amylolytic, including Succinimonas amylolytica, Succinivibrio dextrinosolvens and Ruminobacter amylophilus. But no sequences found to be related in yak clones. The results indicated that the microbials of yak rumen were most related with cellulolytic and the Jinnan cattle's most related with amylolytic. And also, a total of 144 sequences of 184 clones of yak were most similarity with uncultured (or unidentified) rumen bacteriums, but only 127 sequences of 218 clones of Jinnan cattle do so, about 78.26% and 58.25% respectively. A total of 370 sequences of the 16S rDNA clones were deposited in GenBank. 183 clones from yak rumen...
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