In this work, the degradation of several environmental pollutants by Alcaligenes eutrophus JMP134 (pJP4) was studied. It has been reported that this strain grows on 2,4-dichlorophenoxyacetate, 3chlorobenzoate, and phenol, and that it is resistant to Hg2+ toxicity. Except degradation of phenol, all these properties are encoded on pJP4. Although this bacterium was unable to grow on several chlorophenols or chloroguaiacols as sole carbon and energy source, it proliferated in 4-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenoI. Degradation of 2,4,6-trichlorophenoI (up to 0.4 mM) did not depend on the presence of pJP4, since the cured strain JMP222 also expressed this property. In chemostats fed with 2,4,6-trichlorophenoI (0.4 mM) or phenol (1 mM) plus 2,4,5trichlorophenol (0.05 mM), strain JMP134 was able to degrade 2,4,5-trichlorophenoI. On the other hand, strain JMP134 grew at higher levels of HgCI, (0.1 mM) or merbromine (1.5 mM) in rich medium, but growth was not detected in minimal medium cultures, containing either chlorinated or nonchlorinated compounds. The ability of strain JMP134 to survive and degrade chlorphenols in the presence of pulp bleaching effluent was assessed in aerated batch cultures. This biodegradable organic matter-and chlorophenol-containing effluent allowed the proliferation of the strain JMPl34. When 2,4-dichlorophenoxyacetate or 2,4,6-trichlorophenoI was added, complete degradation of these compounds was detected. The degradation was not affected by the presence of indigenous microorganisms or the amount of degradable material. 0 7996 by John Wiley & Sons, ~n c .