Microbial Transformation of Phthalate Esters: Diversity of Hydrolytic Esterases - Environmental Contamination: Health Risks and Ecological Restoration - page 330

COOH

COOCH 3

COOCH 3 COOCH 3

(I) (II)

COOH COOH

COOCH 3

COOCH 3

OH

OH

H

H

OH

OH
(IV) (III)

FIGURE 15.3
The. pathway. of. minor. DMP. biodegradation. by. Micrococcus . sp.. strain. 12B.. (I). dimethyl.
phthalate;. (II). monomethyl. phthalate;. (III). 3,4-dihydro-3,4-dihydroxyphthalate-2-methyl.
ester;. and. (IV). 3,4-dihydroxyphthalate-2-methyl. ester.. (From. Eaton,. R.W.. and. Ribbons,. D.W.,.
J. Bacteriol .,.151(1),.465,.1982.)

bacterium,.different.studies.would.exhibit.distinctively.different.mechanisms.
for. the. same. chemical.. As. a. result,. there. are. still. many. questions. waiting.
to. be. answered. in. terms. of. microbial. behaviors.. Pseudomonads . sp.. capable.
of.degrading.DMP.were.isolated.from.the.environment.(Keyser.et.al..1976),.
such.as. P. luorescens .PHK.and. P. testosteroni ,.which.provide.distinctive.path-
ways. to. the. bacteria.. Both. strains. had. esterase. to. hydrolyze. the. diester. to.
monomethyl. phthalate,. and. then. to. ortho -phthalic. acid. (Figure. 15.3);. ortho -
Phthalate.was.transformed.to.4,5-dihydroxyphthalate,.between.which.there.
was. dihydrodiol,. namely,. cis -4,5-dihydroxy-4,5-dihydrophthalate. yielded.
by.phthalate.4,5-dioxygenase..The.4,5-dihydroxyphthalate.was.decarboxyl-
ated.to.form.protocatechuate,.which.was.processed.at.different.ring.cleavage.
pathways. by. these. two. strains.. A. keyseri . 12B. adopted. a. different. pathway.
via. cis -3,4-dihydroxy-3,4-dihydrophthalate. to. 3,4-dihydroxyphthalate,. then.
to.protocatechuate.(Eaton.2001).(Figure.15.3)..A.minor.degradation.pathway.
for. DMP. was. proposed. via. intermediate. 3,4-dihydro-3,4-dihydroxyphthal-
ate-2-methyl.ester.to.form.3,4-dihydroxyphthalate-2-methyl.ester.(Eaton.and.
Ribbons. 1982). (Figure. 15.4).. According. to. Keyser. et. al.. (1976),. P. testosteroni .
proceeded. via meta -cleavage. to. open. benzene. ring,. whereas. P. luorescens .
proceeded. via. ortho -cleavage. by. protocatechuate. 3,4-dioxygenase. to. form.
3-carboxy- cis ,. cis -muconate,. which. was. further. transformed. generally. to.
β-ketoadipate. (Figure. 15.5).. However,. Keyser. et. al.. did. not. give. detailed.
information. about. the. enzyme. producing. β-ketoadipate.. The. detail. on.
the. derivatives. for. 3-carboxy- cis ,. cis -muconate. was. described. in. another.
report. (Williams. et. al.. 1992),. which. mentioned. the. function. of. enzyme.