Extracellular fructooligosaccharide degradation in Anaerostipes hadrus for co-metabolism with non-fructooligosaccharide utilizers

Butyrate producing bacteria are one of the major components of the human gut microbiota. Their major metabolite, butyrate, has several beneficial properties for host health. Fructooligosaccharides (FOSs) are well documented prebiotics and are hydrolyzed by intracellular glycoside hydrolase family 32 (GH32) enzyme in several butyrate producers, whereas butyrate producers Anaerostipes hadrus and Anaerostipes butyraticus possess extracellular GH32 enzymes. The present study characterized the extracellular GH32 enzymes in the organisms to consider possible cross-feeding of FOSs with other microbes. Culture supernatant of A. hadrus actively hydrolyzed kestose and nystose, i.e., degrees of polymerization 3 and 4 FOSs, respectively, whereas that of A. butyraticus did not hydrolyzed. When co-cultured with Lacticaseibacillus rhamnosus GG in the presence of nystose, which was negative for growth on the FOSs but positive for growth on FOS degradants, A. hadrus promoted the growth of L. rhamnosus GG, but A. butyraticus did not. The observed negative results in A. butyraticus would be due to the presence of a stop codon in the gene encoding extracellular GH32. Genomic analysis revealed that A. hadrus conserved a single extracellular GH32 enzyme at the species level. The enzyme was phylogenetically distinguished into two groups, but the two groups shared similar FOS degradation properties. The results obtained here suggested that A. hadrus is active for extracellular degradation of FOSs and provides its degradants to other microbes. This study provides a basis of knowledge to understand how ingested FOSs are cometabolized in gut microbiota. (C) 2022 Published by Elsevier Inc.

Automated summary

Butyrate-producing bacteria, such as Anaerostipes hadrus, possess extracellular GH32 enzymes that can hydrolyze fructooligosaccharides (FOSs) and provide their degradation products to other microbes. In contrast, Anaerostipes butyraticus lacks this ability due to a stop codon in the gene encoding extracellular GH32. This study contributes to our understanding of how ingested FOSs are metabolized in the gut microbiota.