Ecology/environmental microbiologyProkaryote diversity in the rumen of yak (Bos grunniens) and Jinnan cattle (Bos taurus) estimated by 16S rDNA homology analyses
Introduction
It is well known that ruminants depend on their rumen microorganisms to digest fiber-based diets [1], [2]. During the last 50 years, some rumen bacteria have been isolated and identified. Recently several works [3], [4], [5], [6], [7], [8] estimated the rumen bacterial composition of cow and cattle by means of the sequence analysis of 16S rDNAs retrieved from rumens, and even the transition pattern of the bacterial community corresponding to diet shifting of the hosts [9]. These works showed that the majority of the retrieved rumen 16S rDNAs, although affiliated to the phyla of low G+C Gram-positive bacteria (LGCGPB) and Cytophaga–Flavobacter–Bacteroides (CFB, mainly Bacteroidetes), had less than 97% similarities with the cultured rumen species, indicating that the main portion of rumen bacteria had not yet been cultured. The organisms bearing the sequences low than 90% similarities might represent new phyla or subphyla of bacteria.
Different kind of ruminants, due to the diet and inhabiting environment variation, could harbor a distinct population of rumen bacteria. Yak (Bos grunniens), a kind of ruminant differentiated from others about 2.2 million years ago, is living exclusively on Qinghai–Tibetan Plateau, China, at the height of above 3000 m of sea level. They are important for local people in providing transportation, milk and meat. Since the shortage of grain in that area, yaks are living in a kind of full-grazing style with grasses as the only feed. Hence it can be postulated that yak's rumen may be populated with a special bacterial flora from other ruminants with grain as the adjunct. However to our knowledge, there is no information at this aspect.
The present work aimed to get insight to the bacterial and archaea population of yak's rumen, and further to deduce the survival strategy of yak just on fibrous diet. Hence two 16S rDNA libraries were constructed, one for yak’ rumen and another for Jinnan cattle rumen in comparison of rumen microflora. 16S rDNA homology analysis revealed a significant difference in bacterial composition of the two rumens. Furthermore, some new 16S rDNA sequences without relationship to any cultured bacterial groups were retrieved from yak's rumen.
Section snippets
Animal diets and rumen sampling
Yaks, going to be sampled, were full grazing on Qilian Mountain of Gansu province, China, at the height of 2900–3300 m of sea level. The natural grasslands consisted of sedge and grass. The main species in the sedge were Carex atrofusca, Kobresia humilis, Kobresia capillifolia and Kobresia pygmaea, the cellulose and crude protein of them ranged 20.16–35.34% and 8.3–14.38% (dry-matter basis), respectively. Grass species were Elymus nutans, Roegnevia kamoji, Stipa aliene and Koeleria litwinowi,
VFA composition of the rumen fluids
Short chain VFAs in the rumen fluids were determined as follows, 51.30 mM acetic acid, 27.25 mM propionic acid and 9.34 mM butyric acid in yak rumen, while 78.20 mM acetic acid, 15.11 mM propionic acid and 9.60 mM butyric acid in Jinnan cattle. Obviously, propionic acid in yak rumen was almost as twice as in cattle rumen.
Construction of 16S rDNA libraries
Partial 16S rDNAs in length of 1.0 kb were amplified from the DNAs extracted directly from rumen contents and cloned into a T-vector. Two 16S rDNA gene libraries were constructed, one
Discussion
To get insight of the rumen microbial composition of yak, a kind of ruminant living exclusively in the high plateau, the 16S rDNA library was constructed and the sequence diversity was compared with that of a kind of cattle in the present work. It was just as anticipated that, living as a kind of full-grazing ruminant exclusively on grasses without addition of cereal, yak did harbor a distinct rumen flora and large portion of the 16S rDNA sequences of it was not related to the cultured
Acknowledgments
This study was supported by the grants of the NSFC 30025001 and the innovation program (field frontier) from Chinese Academy of Sciences.
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The uniqueness and superiority of energy utilization in yaks compared with cattle in the highlands: A review
2023, Animal NutritionCitation Excerpt :In summary, it is speculated that the differences in methane production between yaks and cattle could possibly be attributed to: 1) the different structure of ruminal methanogens in yaks, and 2) the lack of substrates for methanogenesis due to a smaller number of bacterial H2 producers. It is worth noting that the number of unclassified bacterial species in the rumen of yaks was double the number in cattle (An et al., 2005), which would also affect bacterial metabolic processes in yaks and needs to be further investigated. Yaks have evolved notably different gut function to other ruminants, possessing a greater density of ruminal papillae in the rumen epithelium and more pleats in the mucosa surface of their abomasum compared with cattle (Beiranvand et al., 2014; Wang et al., 2015), which increases the surface area of the gastrointestinal tract and improves absorptive capacity.