In the animal gut resides the microbiota, a large and diverse community of microorganism, dominated by bacteria, known to have a critical role in the evolution of the intestinal functions and possess a lot of beneficial effects on host health and performance. Specifically, the microbiota is involved in the supply of nutrients, especially in herbivorous species, and in the stimulation of the immune response and protection against pathogens. This intestine consists of various segments and the extent of food digestion in different at each segment. The total bacterial counts in the hindgut (cecum and colon) reach 10¹² cells g^-1 digesta in the intestinal tracts and that number far exceeded the host body cell number.

The composition of the daily diets is a fundamental determinant of what we could get from the food. The digestion of starch and fibre is definitely different. It has been concluded that contents from the cecum and colon (hindgut) had greater potential to digest fibre than those from the jejunum and ileum (small intestine), and CEL (cellulose) is more easily to be digested than NDF (neutral detergent fibre). However, the reason why this happens remains unclear.

Recently, a team of researchers, led by TAN Zhiliang, at the Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA) hypothesized that this phenomenon is related to the microbes, as well as gut region (jejunum, ileum, cecum and colon) and fibre structure (NDF and CEL) could affect bacterial diversity and population of functional bacterial species. And the study was designed to test this hypothesis using in vitro cultivation system.

In this study, three goats were slaughter to provide in vitro inocula from different gut regions. The design of this experiment was a split plot design with gut regions (jejunum, ileum, cecum and colon) as main plot, and substrates (NDF and CEL, 0.4 g) as subplot. Also, four time points (12, 24, 48 and 72 h) were selected to explore the kinetic changes in the intestinal bacterial diversity and functional bacterial species. The microbial samples were collected. DNA was isolated from in vitro culture fluids, PCR-denaturing gradient gel electrophoresis (DGGE) together with quantitative real-time PCR (qPCR) techniques were used to explore the changes in intestinal bacterial diversity and functional bacterial species.

"The results showed that gut region could affect bacterial diversity while fibre structure could not. These are reflected by the fact that the numbers of total bacteria, cellulolytic bacteria, genus Prevotella and amylolytic bacteria in the hindgut inocula were greater than those in the small intestinal inocula. Fiber structure did not significantly influence the dominant bacterial diversity and the numbers of most examined functional bacterial species.” said JIAO Jinzhen, a phD student at ISA and first author on the paper.” “Also, changes in cellulolytic bacterial populations were not coordinative with alteration of fiber disappearance as well as CMCase and xylanase activities, which means that total bacteria while not celluloytic bacteria account for fibre digestion.”

"These findings suggest that fibre digestion in the intestine is related to microbial diversity. The reason why the hindgut contents have greater potential to digest fibre than small intestinal contents is that the former had greater number of total bacteria and functional bacterial species. Furthermore, cellulolytic bacteria are of significant value at the initial stage of fiber digestion among the fiber digestive microbes in the intestine.” said JIAO Jinzhen.

This research was supported by funding from “Strategic Priority Research Programe Climate Change: Carbon Budget and Relevant Issues” of Chinese Academy of Sciences (Grant No. XDA05020700), the National Natural Science Foundation of China (Grant Nos. 31001023, 31201826, 31320103917), “K.C.Wong Education Foundation of CAS” and CAS Visiting Professorship for Senior International Scientists (Grant No. 2010T2S13). And the study entitled “In vitro evaluation of effects of gut region and fibre structure on the intestinal dominant bacterial diversity and functional bacterial species” has been published in the August issue of Anaerobe, details could be found at http://www.sciencedirect.com/science/article/pii/S107599641400081X