Monitoring of gene expression in Fibrobacter succinogenes S85 under the co-culture with non-fibrolytic ruminal bacteria.

Fibrobacter succinogenes is one of the most pivotal fibrolytic bacterial species in the rumen. In a previous study, we confirmed enhancement of fiber digestion in a co-culture of F. succinogenes S85 with non-fibrolytic ruminal strains R-25 and/or Selenomonas ruminantium S137. In the present study, mRNA expression level of selected functional genes in the genome of F. succinogenes S85 was monitored by real-time RT-PCR. Growth profile of F. succinogenes S85 was similar in both the monoculture and co-cultures with non-fibrolytics. However, expression of 16S rRNA gene of F. succinogenes S85 in the co-culture was higher (P < 0.01) than that of the monoculture. This finding suggests that metabolic activity of F. succinogenes S85 was enhanced by coexistence with strains R-25 and/or S. ruminantium S137. The mRNA expression of fumarate reductase and glycoside hydrolase genes was up-regulated (P < 0.01) when F. succinogenes S85 was co-cultured with non-fibrolytics. These results indicate the enhancement of succinate production and fiber hydrolysis by F. succinogenes S85 in co-cultures of S. ruminantium and R-25 strains.

Food Starch Structure Impacts Gut Microbiome Composition.

Starch is a major source of energy in the human diet and is consumed in diverse forms. Resistant starch (RS) escapes small intestinal digestion and is fermented in the colon by the resident microbiota, with beneficial impacts on colonic function and host health, but the impacts of the micro- and nanoscale structure of different physical forms of food starch on the broader microbial community have not been described previously. Here, we use a porcine in vitro fermentation model to establish that starch structure dramatically impacts microbiome composition, including the key amylolytic species, and markedly alters both digestion kinetics and fermentation outcomes. We show that three characteristic food forms of starch that survive digestion in the small intestine each give rise to substantial and distinct changes in the microbiome and in fermentation products. Our results highlight the complexity of starch fermentation processes and indicate that not all forms of RS in foods are degraded or fermented in the same way. This work points the way for the design of RS with tailored degradation by defined microbial communities, informed by an understanding of how substrate structure influences the gut microbiome, to improve nutritive value and/or health benefits.IMPORTANCE Dietary starch is a major component in the human diet. A proportion of the starch in our diet escapes digestion in the small intestine and is fermented in the colon. In this study, we use a model of the colon, seeded with porcine feces, in which we investigate the fermentation of a variety of starches with structures typical of those found in foods. We show that the microbial community changes over time in our model colon are highly dependent on the structure of the substrate and how accessible the starch is to colonic microbes. These findings have important implications for how we classify starches reaching the colon and for the design of foods with improved nutritional properties.