Metaproteome analysis and molecular genetics of rat intestinal microbiota reveals section and localization resolved species distribution and enzymatic functionalities

The digestion of food ingredients depends on the action of the gut microbiota and has a significant influence on the health, especially in the case of metabolic diseases, of the host organism. Despite the relevance of the structure and functionalities in the microbiota for the metabolism of the host, the spatial resolution of microbial consortia and the functionalities in the different gut sections of the rat are mostly unknown. Since there are suitable rat models for human metabolic diseases, the microbiota of the rat is of special interest. Samples along the intestinal tract of rats were investigated using metaproteomics and 16S rRNA gene pyrosequencing. The procedures for harvesting bacteria from the mucus and the content of the gut sections and feces were optimized leading to 2802 nonredundant bacterial protein groups in total that were assigned to spectra measured by liquid chromatography-tandem mass spectrometry. The majority of 16S rRNA genes and protein groups belonged to members of Firmicutes, Bacteroidetes and Proteobacteria. The functionalities in the enzyme repertoire were compared between the mucus and the content of the large intestine sections and the feces samples. This spatial resolution allowed pinpointing changes in the community to specific metabolic capacities like carbohydrate transport and energy conservation. The results showed that the mere analysis of feces samples reflects the functions of the gut microbiota only to a minor extent and sheds light on the metabolic interchange between the microbiota and the host organism.