The metabolism of halogen-substituted benzoic acids by Pseudomonas fluorescens

1. Washed suspensions of Pseudomonas fluorescens, grown with benzoate as sole carbon source, oxidize monohalogenobenzoates in the following descending order of effectiveness: benzoate, fluorobenzoates, chlorobenzoates, bromobenzoates, iodobenzoates. 2. Cells grown on asparagine oxidize benzoate after an adaptive period of 90–120min. This adaptive period is increased by halogenobenzoates in the following approximate descending order of effectiveness: chlorobenzoates, fluorobenzoates (=bromobenzoates), iodobenzoates. This inhibition of adaptation by halogeno analogues depends on the concentration of benzoate and is thus apparently competitive. 3. Cells do not adapt to oxidize the halobenzoates when the halogeno analogues are inducers. However, the fluorobenzoates reduce the lag period taken to form the benzoate-oxidizing system. 4. The halogenobenzoates inhibit adaptation to citrate and nicotinate but not so effectively as benzoate itself. This is presumably a `diauxic' effect. The analogues do not inhibit adaptation to catechol. 5. The halogenobenzoates are not used as sole carbon source for growth nor do they increase growth when cells grow with asparagine as the main carbon source. 6. It is suggested that this inability to use the analogues for growth is due partly to inability of the cells to liberate the halogen and to carry the oxidation to a stage at which carbon may be assimilated and partly to the inhibition of the induction of the oxidizing enzymes.