The highlighted nutritional significance of intestinal fungi: alteration of dietary carbohydrate composition triggers the shifts of colonic fungal community in a pig model.

Carbohydrate is the most important energy source in the diet of human and animals. A large number of studies have shown that dietary carbohydrates (DCHO) are related to the bacterial community in the gut, but its relationship with the composition of intestinal fungi is still unknown. Here, we report the response of colonic fungal community to different composition of DCHO in a pig model. Three factors, ratio of (2:1, 1:1 and 1:2) amylose to amylopectin (AM/AP), level of non-starch polysaccharides (NSP, 1%, 2% and 3%) and mannan-oligosaccharide (MOS, 400, 800 and 1,200 mg/kg), were considered according to a L9 (34) orthogonal design to form nine diets with different carbohydrate composition. Sequencing based on an Illumina HiSeq 2500 platform targeting the internal transcribed spacer 1 region showed that the fungal community in the colon of the pigs responded to DCHO in the order of MOS, AM/AP and NSP. A large part of some low-abundance fungal genera correlated with the composition of DCHO, represented by Saccharomycopsis, Mrakia, Wallemia, Cantharellus, Eruotium, Solicoccozyma and Penicillium, were also associated with the concentration of glucose and fructose, as well as the activity of β-D-Glucosidase in the colonic digesta, suggesting a role of these fungi in the degradation of DCHO in the colon of pigs. Our study provides direct evidences for the relationship between the composition of DCHO and fungal community in the colon of pigs, which is helpful to understand the function of gut microorganisms in pigs.ImportanceAlthough fungi are a large group of microorganisms besides bacteria and archaea in the gut of monogastric animals, the nutritional significance of fungi has been ignored for a long time. Our previous studies have revealed a distinct fungal community in the gut of grazing Tibetan pigs, and a close correlation between fungal species and short-chain fatty acids, the main microbial metabolites of carbohydrates in the hindgut of pigs. These groundbreaking findings indicate a potential relationship between intestinal fungi and the utilization of DCHO. However, no evidence directly proves the response of intestinal fungi to changes in DCHO. Here, we show a clear alteration of colonic fungal community in pigs triggered by different composition of DCHO simulated by varied concentrations of starch, NSP and oligosaccharides. Our results highlight the potential involvement of intestinal fungi in the utilization of nutrients in monogastric animals.