Formate as electron carrier in the gut acetogen <i>Blautia luti</i> : a model for electron transfer in the gut microbiome

Species of the genus <i>Blautia</i> are commonly found in the human gut and are known to be beneficial for the human well-being. However, only little is known about the physiology and the specific role of <i>Blautia</i> species in the human gut. In this study, we investigated the heterotrophic metabolism of the formate dehydrogenase lacking gut acetogen <i>Blautia luti</i>. We identified acetate, succinate, lactate, formate, and hydrogen as end products of sugar fermentation. Interestingly, formate is produced by the pyruvate-formate lyase reaction and used as electron acceptor in the Wood-Ljungdahl pathway of CO₂ fixation. Thus, formate connects the oxidative branch of glucose metabolism with the reductive branch. The use of formate as an intraspecies electron carrier seems to be common in gut acetogens. This study highlights the role of formate as electron carrier in the gut microbiome and improves our understanding of the physiology of <i>Blautia</i> species in the human gut. It also introduces <i>B. luti</i> as potential candidate for biotechnological applications due to the production of highly desired succinate.