Incomplete Wood–Ljungdahl pathway facilitates one-carbon metabolism in organohalide-respiring Dehalococcoides mccartyi

Abstract

Significance We have studied the functionality of an incomplete acetyl-CoA “Wood–Ljungdahl” pathway in a strictly organohalide-respiring bacterium, Dehalococcoides mccartyi . We found that in addition to its ability to incorporate exogenous formate, this pathway cleaves acetyl-CoA to generate methyl-tetrahydrofolate for methionine biosynthesis, serving as a unique substitute of the missing methylene-tetrahydrofolate reductase function. We also found that accumulation of carbon monoxide (CO), an obligate by-product from acetyl-CoA cleavage, inhibits D. mccartyi axenic cultures, but can be ameliorated by the presence of a CO-oxidizing organism, resulting in an unusual syntrophic association. The understanding of the products and biosynthetic functions of this incomplete Wood–Ljungdahl pathway improves our knowledge of alternate central metabolic strategies used by environmental microorganisms.