Cleavage of the ether bond of chlorophenoxyalkanoate herbicides is catalyzed by an α-ketoglutarate-linked dioxygenase (TfdA). In this step, α-ketoglutarate is decarboxylated to succinate and must be regenerated for continual substrate cleavage. Limitations in herbicide degradation are to be expected in the case of a shortage of α-ketoglutarate. Such a situation was simulated and studied with Delftia (formerly Comamonas) acidovorans MC1 and Rhodoferax sp. P230, which constitutively express etherolytic dioxygenase activity by excreting 2,4-dichlorophenol (DCP) as a dead-end product. The results showed that 2,4-dichlorophenoxyacetate (2,4-D) could hardly be cleaved under these conditions which is attributed to the inability to regenerate α-ketoglutarate from the cleavage products, i.e. succinate and glyoxylate [1 ]. With pyruvate, in contrast, liberated as the oxidized alkanoic acid from the cleavage of (RS )-2-(2,4-dichlorophenoxy)propionate (2,4-DP), the regeneration of α -ketoglutarate seems to be guaranteed from succinate as resulted from the utilization of 2,4-DP to a considerable amount under these conditions. The extent was limited, however, which was apparently caused by the accumulation of DCP. Continual cleavage of 2,4-DP could be demonstrated in the presence of Ochrobactrum sp. K2-14, which functions as a DCP-consuming strain. Addition of extra metabolites, i.e. α-ketoglutarate or other readily metabolizable substrates, improved the cleavage of the herbicides. This was most pronounced with 2,4-D that was found now to be also utilized to a considerable extent. Conversely, the cleavage of the herbicides (2,4-DP) was reduced and ultimately ceased with cells depleted by starvation of the pool of metabolites. Again, this deficit could be restored by adding α-ketoglutarate. The limitations in utilizing phenoxyalkanoate herbicides are discussed in terms of pseudo-recalcitrance owing to deficits in metabolites (α-ketoglutarate) rather than enzyme activity (TfdA).