Beta-glucan is a major growth substrate for human gut bacteria related to Coprococcus eutactus

A clone encoding carboxymethylcellulase activity was isolated during functional screening of a human gut metagenomic library using Lactococcus lactis MG1363 as heterologous host. The insert sequence revealed a glycoside hydrolase family 9 (GH9) catalytic domain with sequence similarity to a gene from Coprococcus sp. ART55/1, which is closely related to Coprocococcus eutactus. Surveys of available genomes indicated a limited distribution of GH9 domains among dominant human colonic anaerobes. Genomes of two Coprococcus-related strains showed the presence of two GH9-encoding and four GH5-encoding genes, however, the strains did not appear to be able to degrade cellulose. Instead, they grew well on beta-glucans and one of the strains also showed growth on galactomannan, galactan and glucomannan. Gene expression and proteomic analysis of Coprococcus sp. ART55/1 grown on cellobiose, beta-glucan and lichenan led to a similar change in expression in comparison to glucose. On beta-glucan and lichenan only, one of the four GH5 genes was strongly upregulated. Growth on glucomannan lead to a transcriptional response of many genes, in particular a strong upregulation of glycoside hydrolases involved in mannan degradation. Thus, beta-glucans are a major growth substrate for species related to Coprococcus eutactus, with glucomannan and galactans alternative substrates for some strains.