Introduction: The gut microbiome is a very complex community not only involved in the digestion of nutrients but also plays a role in developing diseases as well as in human well-being. Gut acetogens such as Blautia strains are often connected to the human well-being[1]. However, only little is known about the physiology of different Blautia species. In this study, we characterized the degradation pathway of myo-inositol, an abundant sugar of the human body, by the acetogen Blautia schinkii.

Goals: To unravel the myo-inositol degradation pathway of B. schinkii.

Materials & Methods: Growth experiments, fermentation and metabolite analyses, enzyme assays, genome analysis and analysis of gene expression

Results: B. schinkii can grow on myo-inositol as carbon and energy source. Myo-inositol is first oxidized by an inositol dehydrogenase and then further converted via a dehydratase and kinase to 2-deoxy-5-keto-D-gluconic acid 6-phosphate (DKGP). DKGP is then split by an aldolase into dihydroxyacetone (DHA) and malonate semialdehyde. DHA is metabolized to acetate and ethanol. Interestingly, malonate semialdehyde is reduced to the unusual product 3-hydroxypropionate (3HP). The highest yield of 3HP produced by B. schinkii was 22 mM. Furthermore, we could identify the NADH-dependent 3HP dehydrogenase, the key enzyme in 3HP production.

Summary: The human gut acetogen B. schinkii produces the valuable product 3-hydroxypropionate from myo-inositol, presenting a novel feature of acetogenic gut bacteria that might be of relevance not only for the human well-being but also for bioindustrial applications.

[1] Liu X., Mao, B., Gu, J., Cui, S., Wang, G., Zhao, J., Zhang, H., Chen, W. (2021) Gut Microbes 13: e1875796