| Summary: | Abstract Background Both phylogeny and functional capabilities within the gut microbiota populations are of great importance for influencing host health. As a novel type of resistant starch, transglycosylated starch (TGS) modifies the microbial community and metabolite profiles along the porcine gut, but little is known about the related functional adaptations in key metabolic pathways and their taxonomic identity. Results Metagenomic sequencing was used to characterize the functional alterations in the cecal and colonic microbiomes of growing pigs fed TGS or control starch (CON) diets for 10 days (n = 8/diet). Bacterial communities were clearly distinguishable at taxonomic and functional level based on the dietary starch, with effects being similar at both gut sites. Cecal and colonic samples from TGS-fed pigs were enriched in Prevotella, Bacteroides, Acidaminoccus and Veillonella, whereas Treponema, Ruminococcus, and Aeromonas declined at both gut sites compared to CON-fed pigs (log2 fold change > ±1; p < 0.001 (q < 0.05)). This was associated with increased enzymatic capacities for amino acid metabolism, galactose, fructose and mannose metabolism, pentose and glucuronate interconversions, citrate cycle and vitamin metabolism for samples from TGS-fed pigs. However, TGS-fed pigs comprised fewer reads for starch and sucrose metabolism and genetic information processing. Changes in key catabolic steps were found to be the result of changes in taxa associated with each type of starch. Functional analysis indicated steps in the breakdown of TGS by the action of α- and β-galactosidases, which mainly belonged to Bacteroides and Prevotella. Reads mapped to alpha-amylase were less frequent in TGS- compared to CON-fed pigs, with the major source of this gene pool being Bacillus, Aeromonas and Streptococcus. Due to the taxonomic shifts, gene abundances of potent stimulants of the mucosal innate immune response were altered by the starches. The cecal and colonic metagenomes of TGS-fed pigs comprised more reads annotated in lipopolysaccharides biosynthesis, whereas they became depleted of genes for flagellar assembly compared to CON-fed pigs. Conclusions Metagenomic sequencing revealed distinct cecal and colonic bacterial communities in CON- and TGS-fed pigs, with strong discrimination among samples by functional capacities related to the respective starch in each pig’s diet.
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