Anaerobic degradation of 3-halobenzoates by a denitrifying bacterium

A denitrifying bacterium was isolated from a river sediment after enrichmen t on 3-chlorobenzoate under anoxic, denitrifying conditions. The bacterium, designated strain 3CB-1, degraded 3-chlorobenzoate, 3-bromobenzoate, and 3 -iodobenzoate with stoichiometric release of halide under conditions suppor ting anaerobic growth by denitrification. The 3-halobenzoates and 3-hydroxy benzoate were used as growth substrates with nitrate as the terminal electi on acceptor. The doubling time when growing on 3-halobenzoates ranged from 18 to 25 h. On agar plates with 1 mM 3-chlorobenzoate as the sole carbon so urce and 30 mM nitrate as the electron acceptor, strain 3CB-1 formed small colonies (1-2 mm in diameter) in 2 to 3 weeks, Anaerobic degradation of bot h 3-chlorobenzoate and 3-hydroxybenzoate was dependent on nitrate as an ele ctron acceptor and resulted in nitrate reduction corresponding to the stoic hiometric values for complete oxidation of the substrate to CO2. 3-Chlorobe nzoate was not degraded in the presence of oxygen. 3-Bromobenzoate and 3-io dobenzoate were also degraded under denitrifying conditions with stoichiome tric release of halide, but 3-fluorobenzoate was not utilized by the bacter ium. Utilization of 3-chlorobenzoate was inducible, while synthesis of enzy mes for 3-hydroxybenzoate degradation was constitutively low, but inducible . Degradation was specific to the position of the halogen substituent, and strain 3CB-1 did not utilize 2- or - 4-chlorobenzoate.