Microbial degradation of sparingly soluble organic chemicals: Phthalate esters

Strains of Mycobacterium and Nocardia isolated because of their ability to use di(2‒ethylhexyl) phthalate (DEHP) as sole carbon source also grew on diethyl, diisooctyl, and butyl benzyl phthalates. As the two bacteria grew on DEHP, they excreted products that increased the solubility of DEHP and diisooctyl, dihexyl, and diisodecyl but not butyl benzyl or di‒n‒butyl phthalates. The solubilizer was produced by Mycobacterium sp. even when grown on a water‒soluble substrate such as acetate. Addition of the solubilizer to culture media enhanced the degradation of DEHP and diisooctyl phthalate by Mycobacterium sp. and Nocardia sp. but not butyl benzyl phthalate. The extent of DEHP degradation by Mycobacterium sp. in media amended with the solubilizer was reduced and the initiation of degradation was delayed if the solubilizer was first treated with protease. The effect of protease was not a result of its toxicity to Mycobacterium or use of the enzyme preparation for growth of the organism. The results thus show that microbial products increase the solubility of certain phthalates and enhance their degradation.