Visualization of microbe-dietary remnant interactions in digesta from pigs, by fluorescence in situ hybridization and staining methods; effects of a dietary arabinoxylan-rich wheat fraction

Abstract

This study investigated how the addition of a specific hydrocolloid, arabinoxylan (AX), to the pig diets containing red meat, affected the gut microbiota in terms of changes to the bacterial community dynamics. Fluorescence in situ hybridization (FISH) was used to enumerate both broad groups and particular bacterial species, and showed systematic differences in pigs fed AX. In addition, the role of bacteria in the fermentation of dietary substrates was studied by visualizing direct associations between the bacteria and substrate particles. To achieve this, novel methods of combining histological staining or enzymatic labelling with FISH protocols were established. In this way, undigested and/or unfermented remnants of meat, endogenous mucin, and several plant cell wall hydrocolloids (cellulose, lignin and arabinoxylan) were distinguished, together with large intestine microbiota under brightfield and/or confocal laser scanning microscopy (CLSM). It was evident that no apparent direct associations occurred between specific classes or groups of bacteria and meat, mucin, lignin or AX remnants. In contrast, bacteria belonging to Clostridium clusters XIVa and XIVb formed a strong (P < 0.01) direct association with cellulose remnants in the pig digesta in the caecum.