Degradation of 3-phenylpropionic acid by Haloferax sp. D1227

Haloferax sp. D1227, isolated from soil contaminated with highly saline oil brine, is the first halophilic archaeon to demonstrate the utilization of aromatic compounds (i.e., benzoic acid, cinnamic acid, and 3-phenylpropionic acid) as sole carbon and energy sources for growth. The degradation of 3-phenylpropionic acid in this strain was studied to examine the strategies utilized by Archaea to metabolize aromatic compounds. Based on our findings of (1) the extracellular accumulation of cinnamic acid, benzoic acid, 3-hydroxybenzoic acid, and gentisic acid in cultures of Haloferax D 1227 grown on 3-phenylpropionic acid, (2) the presence of an 3-phenylpropionylCoA dehydrogenase, (3) the ATP, CoA, and NAD-dependent conversion of cinnamic acid to benzoylCoA, and (4) the presence of gentisate 1,2-dioxygenase, we propose that Haloferax D1227 metabolizes 3-phenylpropionic acid by initial 2-carbon shortening of the side chain to benzoylCoA via a mechanism similar to fatty acid beta-oxidation, followed by aromatic degradation using a gentisate pathway. The upper aliphatic pathway from 3-phenylpropionic acid to benzoic acid is regulated separately from the lower gentisate pathway.