Metabolic pathway to propionate of Pectinatus frisingensis, a strictly anaerobic beer-spoilage bacterium

Abstract

Pectinatus frisingensis, a recently described species of anaerobic mesophilic beer-spoilage bacteria, grows by fermenting various organic compounds, and produces mainly propionate, acetate, and succinate. Although acrylate and succinate were both dismutated by dense resting-cell suspensions, propionate production proceeded through the succinate pathway: [3-¹³C]pyruvate consumption led to equal ¹³C-labeling of propionate on methyl and methylene groups. Growth on glucose or glycerol led to a similar propionate to acetate ratio, suggesting dihydroxyacetone phosphate as being a common metabolic intermediate. Diacetyl, 1,3-propanediol, and 2,3-butanediol were not growth substrates or fermentation products, but they were all dismutated by dense resting-cells suspensions to acetate and propionate. Acetoin was a minor fermentation product. The consumption of [2-¹³C] or [3-¹³C]pyruvate by dense resting-cell suspensions demonstrated the involvement of two equivalent pyruvate molecules during acetoin production. Key enzymes involved in this metabolism were measured in anoxic cell-free extracts. A tentative metabolic pathway to the main fermentation products was proposed from the above results.