The growth of Alkaliflexus imshenetskii and concentrations of metabolites produced by this microorganism during growth on various organic substrates were studied. It was shown that, although the composition and quantitative ratios of the fermentation products depended on the substrates utilized, acetate and succinate were always the major metabolites, while only minor amounts of formate were produced. During growth on xylan and starch, diauxy was observed caused by the successive decomposition of oligosaccharides and monosaccharides. It was demonstrated that, when grown on cellobiose, A. imshenetskii is capable of succinate fermentation mediated by phosphoenolpyruvate carboxykinase, pyruvate kinase, fumarate reductase, pyruvate ferredoxin oxidoreductase, malate dehydrogenase, and methylmalonyl-CoA decarboxylase. Succinate may be both the intermediate and final product of the A. imshenetskii metabolism, being fermented to propionate by methylmalonyl-CoA decarboxylase.