Phthalate Family Pathway Map

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This pathway was contributed by Brian Burke, Shane M. Cain, Meaghan Fitzgerald, Stephen Stephens, Michael Turnbull and Sujana Mittapalli University of Minnesota.

Phthalic acid diesters, also called phthalates, are used industrially in the production of a variety of household and consumer goods including plastic polymers, lubricating oils, and carriers for perfumes in cosmetics. Because of their widespread use, phthalates have become one of the most abundant industrial pollutants in the environment. Several phthalates are classified as toxic chemicals in the EPA's Toxics Release Inventory Program.

Phthalic acid (phthalate) is used industrially as a plasticizer. Terephthalate is used in the synthesis of polyethylene terephthalate (abbreviated PET or PETE), a plastic polymer with many commercial uses including the production of plastic beverage bottles.

Phthalates in the environment show a moderate resistance to bacterial degradation, but are easily degraded in the laboratory. Pseudomonas cepacia, Mycobacterium vanbaalenii PYR-1, and Arthrobacter keyseri 12B all convert phthalate to a cis-dihydrodiol. Ps. cepacia produces the 4,5-dihydrodiol (Ballou & Batie, 1988), and M. vanbaalenii PYR-1 (Kim et al., 2007) and A. keyseri 12B (Eaton, 2001) produce the 2,3-dihydrodiol. These are transformed into the respective dihydroxy compounds, both of which can be decarboxylated to 3,4-dihydroxybenzoate (protocatechuate). Comanonas testosteroni strains can convert terephthalate (Wang et al., 1995) and 4-hydroxyphthalate (Nakazawa & Hayashi, 1978) to protocatechuate. A Micrococcus sp. strain can decarboxylate 3,4-dihydroxyphthalate to 2,3-dihydroxybenzoate (Eaton & Ribbons, 1982).

Rhodococcus jostii RHA1 is able to use monoalkyl esters including methyl, butyl, hexyl and 2-ethylhexyl phthalates as its sole carbon and energy source. Suspensions of cells grown on phthalate could degrade dimethyl, diethyl, dipropyl, dibutyl, dihexyl and di-(2-ethylhexyl) phthalates. The major metabolites of the dialkyl esters are corresponding monoalkyl esters and phthalate. Demethylation of the alkyl side chains was also observed as a concurrent minor process. The degradation of dibutyl phthalate is provided here as an example and other phthalate esters follow similar pathways (Hirofumi et al., 2010). The biodegradation of dimethylisophthalate ester, another model phthalate ester, is found elsewhere.

The following is a text-format phthalate pathway map. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic (15k) format.

                                                                                                                   Dibutyl phthalate
                                                                                                                   Rhodococcus jostii
                                                                                                                            | dibutyl
                                                                                                                            | phthalate
                                                                                                             monobutyl      | hydrolase
                                                                                                             phthalate      |
                                                     from the                                                hydrolase      v
                                               Phenanthrene Pathway -----> Phthalate             Phthalate <----------- Monobutyl
                                                 Fluorene Pathway         Pseudomonas           Arthrobacter            phthalate
                                                Anthracene Pathway          cepacia             keyseri 12B
                                            Fungal Anthracene Pathway          |      Mycobacterium vanbaalenii PYR-1
                                                                               |                     |
                                                                phthalate 4,5- |                     | phthalate 3,4-
                                                                   dioxygenase |                     | dioxygenase
                                                                               |                     |
                                                                               v                     v
 Benzoate <-------- Terephthalate           4-Hydroxyphthalate          Phthalate 4,5-        Phthalate 3,4-
(anaerobic)        C. testosteroni               Comamonas              cis-dihydrodiol       cis-dihydrodiol
  Pathway               YZW-D               testosteroni NH1000         C. testosteroni              |
                          |                          |                         |                     |
                          |                          |                         |                     |
            terephthalate |           4,5-dihydroxy- |          phthalate 4,5- |                     | phthalate 3,4-
          1,2-dioxygenase |                phthalate |         cis-dihydrodiol |                     | cis-dihydrodiol
                          |            decarboxylase |           dehydrogenase |                     | dehydrogenase
                          |                          |                         |                     |
                          |                          |                         |                     |
                          v                          v                         v                     v       Micrococcus sp. 3
                  Terephthalate 1,2-         3-Hydroxybenzoate           4,5-Dihydroxy-        3,4-Dihydroxy- ---------------+
                   cis-dihydrodiol                   |                     phthalate             phthalate                   |
                          |                          |                         |                     |                       | 3,4-dihydroxy-
       terephthalate 1,2- |        3-hydroxybenzoate |          4,5-dihydroxy- |                     | 3,4-dihydroxy-        | phthalate
          cis-dihydrodiol |            4-hydroxylase |               phthalate |                     | phthalate             | decarboxylase
            dehydrogenase |                          |           decarboxylase |                     | 2-decarboxylase       |
                          |                          |                         |                     |                       v
                          |                          |                         +----------+----------+             2,3-Dihydroxybenzoate
                          |                          |                                    |                                  |
                          +-----------------------+  |  +---------------------------------+                                  |
                                                  |  |  |                                                                    |
                                                  v  v  v                                                                    v
                                           3,4-Dihydroxybenzoate                                                          to the
                                             (Protocatechuate)                                                        2-Aminobenzoate
                                                     |                                                                    Pathway
                                                  to the

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Page Author(s): Brian Burke, Shane M. Cain, Stephen Stephens, Meaghan Fitzgerald, Michael Turnbull and Sujana Mittapalli

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