Erythritol Metabolism by Propionibacterium pentosaceum

Randomly labeled erythritol-14C has been synthesized and incubated with fluoride-poisoned suspensions of dried cells of Propionibacterium pentosaceum. Therefrom labeled glycerol-3-P, glyceric acid-3-P, erythritol-1-P, ribose-5-P, xylulose-5-P, glucose-6-P, fructose-6-P, mannose-6-P, fructose-1,6-di-P, and sedoheptulose-7-P were isolated. Erythritol-14C-1-P accumulated more rapidly than did the other phosphates. Even under conditions in which its dephosphorylation is inhibited it was metabolized to the same products as was erythritol-14C. Also, in short term experiments the addition of unlabeled l-erythritol-1-P to cell preparations actively metabolizing erythritol-14C reduced the amount of label normally found as glyceric acid-3-P. This supports the view that in P. pentosaceum erythritol metabolism proceeds via a series of phosphorylated intermediates, of which l-erythritol-1-P is the primary member. l-Erythritol-1-P can serve as hydrogen donor for the reduction of 2,6-dichloroindophenol in cell-free extracts. Although the product of the oxidation was not isolated, indirect evidence suggests that it is l-erythrulose-1-P and that this compound is the next intermediate in the erythritol fermentation. Labeling dilution experiments indicated that d-erythrose-4-P is not a direct intermediate in the sequence. The formation of labeled formaldehyde in the reaction mixtures lends support to the view that l-erythrulose-1-P, formed from l-erythritol-1-P, undergoes cleavage between the C3 and C4 positions to yield formaldehyde and dihydroxyacetone-P. This cleavage, combined with reactions known to occur in the propionic acid bacteria, provides a source of the labeled C3, C5, C6, and C7 sugar phosphates accumulating in the cell suspensions and an explanation for the substantial quantities of formic acid produced in the fermentation of erythritol.