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
RHA1
|
| 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
|
v
to the
Vanillin
Pathway
Page Author(s): Brian Burke, Shane M. Cain, Stephen Stephens, Meaghan Fitzgerald, Michael Turnbull and Sujana Mittapalli
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