Figure 1.

A minimal intestinal microbiome of nine strains performs complete carbohydrate fermentation. a. The trophic cascade of essential metabolic reactions ferments carbohydrates into the end metabolites acetate, propionate, and butyrate. ‘A reactions’ convert primary substrates to intermediate or end metabolites, and ‘B reactions’ convert intermediate metabolites. ‘C-reactions’ consume oxygen and hydrogen that can inhibit fermentative activity. b. The combined metabolic activity of nine selected species covers all essential reactions of the trophic cascade. Five primary degraders produce intermediate metabolites and acetate from primary substrates. Four secondary degraders consume intermediates and produce end metabolites. Hydrogen and oxygen metabolism were attributed to strains using published data. Y: YCFA, M: M2GSC, FO: formate, LT: lactate, SU: succinate, AC: acetate, BU: butyrate, PR: propionate. c. Log fold change of single strains (in gray) and co-cultured strains (PB002; in black) as determined by qPCR for three replicate experiments with three technical replicates from time point 0 h and 48 h with SD. The data are normalized by the 16S rRNA gene copy number of each strain. (†) The starting cell concentration of A. lactatifermentans could not be quantified in the mixed culture, thus the starting concentration of the single cultures was used as a proxy. Culturing was performed in Hungate tubes for single strains and PB002. d. Metabolites produced by either single cultures or the PB002 consortium. Intestine image adapted from Staff, Blausen.com. 2014. WikiJournal of Medicine 1(2).³⁷