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Applied and Environmental Microbiology, September 2002, p. 4684-4688, Vol. 68, No. 9
0099-2240/02/$04.00+0 DOI: 10.1128/AEM.68.9.4684-4688.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Enhanced Degradation of an Endocrine-Disrupting Chemical, Butyl Benzyl Phthalate, by Fusarium oxysporum f. sp. pisi Cutinase
Yang-Hoon Kim,1,2 Jeewon Lee,1* Ji-Young Ahn,1 Man Bock Gu,2 and Seung-Hyeon Moon2
Department of Chemical and Biological Engineering, Korea University, Sungbuk-Ku, Seoul 136-701,1
Department of Environmental Science and Engineering, Kwangju Institute of Science and Technology, Kwangju, South Korea2
Received 13 December 2001/
Accepted 7 June 2002

ABSTRACT
Compared to yeast esterase, fungal cutinase degraded butyl benzyl
phthalate (BBP) far more efficiently; i.e., almost 60% of the
BBP disappeared within 7.5 h. Also, the final chemical composition
significantly depended on the enzyme used. Toxicity monitoring
using bioluminescent bacteria showed that butyl methyl phthalate,
a major product of degradation by esterase, was an oxidative
toxic hazard.

INTRODUCTION
Phthalates are plasticizers used in the manufacture of polyvinyl
chloride and often in paints, lacquers, and cosmetics (
18,
26,
31). Phthalates found in sediment, water, and air (
13) have
also been detected in foods, as they can migrate out of food
packaging materials (
29,
36).
n-Butyl benzyl phthalate (BBP)
is a phthalic ester in papers and paperboards used as packaging
materials for aqueous, fatty, and dry foods (
19,
37). BBP exerted
estrogenic activities in several in vitro tests (
2,
18,
20,
43). During the past 10 years, there have been a series of reports
on the developmental toxicity of BBP in rats (
1,
11,
12,
39),
and the teratogenic effects have also been observed in mice
and chicks (
4,
32).
Cutinase, a hydrolytic enzyme that degrades cutin (a polyester consisting of hydroxy and epoxy fatty acids, usually with n-C16 and n-C18 of higher plants), can, unlike other lipases, show enzymatic activity without interfacial activation. Some microorganisms such as Fusarium oxysporum f. sp. pisi live on cutin as their sole carbon source producing extracellular cutinases, and several bacterial cutinases (Pseudomonas putida, Pseudomonas mendocina, and Corynebacterium spp.) have been isolated and characterized (8, 21, 23, 25, 30, 34, 35). These enzymes have been largely exploited for esterification and transesterification in chemical synthesis (16) and have also been applied in the composition of laundry or dishwashing detergent (14, 28, 38). Other potential uses for cutinase include its application in the oleochemistry industry (6) and in the degradation of plastic (22).
In the present study, we investigated the efficacies of fungal cutinase and yeast esterase in the degradation of BBP. During the enzymatic degradation of BBP, time-course compositional changes of several BBP-derived compounds were monitored. The cellular toxicity of degradation products was also measured by using various bioluminescent bacteria.

Enzymatic degradation of BBP by cutinase and esterase.
Purified cutinase from
F. oxysporum f. sp.
pisi (kindly provided
by C. M. J. Sagt, Utrecht University, Utrecht, The Netherlands)
and commercial
Candida cylindracea esterase (Boehringer Mannheim
GmbH, Mannheim, Germany) were dissolved in Tris-HCl buffer (10
mM, pH 8.0), and the enzyme concentration was adjusted to 10
or 100 mg liter
-1. The enzymatic degradation of BBP (98% purity;
Aldrich, Milwaukee, Wisc.) was begun by adding 50 µl of
the concentrated BBP solution (500 g liter
-1 in pure methanol
[99.9%; Merck, Darmstadt, Germany]) to 50 ml of the enzyme solution
described above in a 250-ml flask and was continued for 3 days
in the dark in a shaking incubator (30°C, 200 rpm).

Analyses of BBP-derived degradation products.
Each time-course sample (500 µl) was mixed with 500 µl
of
n-hexane (>99% purity; Sigma) for 3 h. After phase separation
had been completed, we confirmed that the nonpolar compounds,
including BBP and its derivatives, were successfully extracted
into the hexane phase with almost 100% efficiency. To recover
residual compounds in the aqueous phase (0.1% methanol), the
separated aqueous phase was lyophilized after filtering with
a YM-3 membrane (Amicon, Cambridge, Mass.) to remove enzymes,
followed by the addition of 500 µl of methanol. All chemicals
in
n-hexane or methanol were analyzed using gas chromatography-mass
spectrometry (GC/MS) by injecting a 4-µl sample into an
HP6890 series gas chromatograph-mass selective detector with
helium as the carrier gas at 1 ml min
-1. The temperature at
the injection port was 280°C, and the oven temperature was
programmed to increase from 80°C (for 4 min) to 310°C
(for 5 min) at 7°C min
-1. Data collection and processing
were performed with HP MSD ChemStation software containing the
Wiley chemical library.

Toxicity monitoring of degradation products by using bioluminescent bacteria.
Escherichia coli strain GC2 (
lac::
luxCDABE) has the
luxCDABE gene from
Xenorhabdus luminescens under the control of the
lac promoter. Several other bioluminescent
E. coli strains were
used for evaluating possible modes of toxicity: DPD2794 (
recA::
luxCDABE),
which can be used to detect genotoxicity (
42); TV1016 (
grpE::
luxCDABE),
which is sensitive to protein damage (
41); DPD2511 (
katG::
luxCDABE),
which is sensitive to oxidative damage (
3); and DPD2540 (
fabA::
luxCDABE),
which is sensitive to membrane damage (
7). Each strain was first
cultured in 100 ml of Luria-Bertani medium (37°C and 250
rpm). When the optical density at 600 nm reached 0.8, 0.2-ml
portions of the culture broth were mixed with various test samples
(25 µl), i.e., Tris-HCl buffer (10 mM, pH 8.0) containing
neither enzyme nor BBP, Tris-HCl buffer containing enzyme only
(cutinase [10 mg liter
-1] or esterase [100 mg liter
-1]), Tris-HCl
buffer containing only BBP (500 mg liter
-1), or the final samples
after enzymatic degradation of BBP for 3 days. The recombinant
culture and test sample mixtures were prepared in triplicate
in a highly sensitive 96-well microplate luminometer (Microlite;
Dynex Technologies, Chantilly, Va.) at 30°C, and the emitted
bioluminescence (BL) was measured at a regular time interval,
6 h. The relative BL, i.e., the maximum BL measured with the
final degradation products divided by the maximum BL measured
with only buffer solution containing neither BBP nor enzyme,
was used as a parameter indicating the toxicity of each test
sample.

Enzymatic degradation of BBP: fungal cutinase versus yeast esterase.
With the fungal cutinase (10 mg liter
-1) from
F. oxysporum f.
sp.
pisi, almost 60% of the initial BBP was decomposed within
7.5 h, while with the yeast esterase (from
C. cylindracea),
more than 90% of the initial BBP remained nondegraded even after
3 days of treatment (Fig.
1a). When esterase that was tenfold
more concentrated (100 mg liter
-1) was applied, the BBP concentration
decreased significantly after 3 days (Fig.
1a). The cutinase
or esterase activity in various time-course samples was estimated
by measuring the initial maximum activity with PNB (
p-nitrophenyl
butyrate) as the substrate. During the 72-h process in 0.1%
methanol solution, cutinase (10 mg liter
-1) and esterase (100
mg liter
-1) maintained more than 85% and 80% of the initial
hydrolytic activities, respectively (Fig.
1b). As shown in Fig.
1b, the stability of the cutinase activity was apparently greater
than that of esterase throughout the 3 days of degradation.
The initial BBP breakdown (for 15 min), shown in the semilogarithmic
plot in Fig.
2a, is presumed to follow a first-order kinetics,
i.e.,
dN/
dt = -
KN, where
N and
K represent the residual BBP
amount and the degradation constant, respectively. The estimation
of the degradation constants,
KC10 (for cutinase, 10 mg liter
-1)
and
KE100 (for esterase, 100 mg liter
-1), demonstrated that
the initial BBP degradation by cutinase seemed to proceed more
than 4 times faster than that by esterase (Fig.
2a). This significant
difference in the initial degradation rates seems to have no
correlation with the enzyme stability, because both enzymes
showed almost 100% stability for the initial 15 min (Fig.
2b).
It is noteworthy that more than 30% of the initial BBP was degraded
by cutinase only after 15 min (Fig.
2a).

Formation of BBP-derived chemicals in enzymatic decomposition process.
During biodegradation, GC/MS analysis detected five different
chemicals: butyl methyl phthalate (BMP), dimethyl phthalate
(DMP), benzene methanol (BM), 1,3-isobenzofurandione (IBF),
and an unidentified chemical (X) (Fig.
3 and
4). As shown in
Fig.
3 and
4, the formation of the decomposition products significantly
depended on the enzyme used. In both enzymatic processes, IBF
was rapidly formed as a major product for the initial 7.5 h
but then progressively decreased. While the amount of IBF continued
to decrease after 7.5 h, the amount of BMP continued to increase
in the esterase process and became the most abundant chemical
after 3 days (Fig.
4). In the cutinase process (Fig.
3), the
degradation compounds other than IBF were produced at very low
concentrations.
The important characteristics of the enzymatic degradation of
BBP are schematically summarized in Fig.
5. Approximately 75%
of the total degraded amount of BBP was degraded during the
initial 7.5 h and was simultaneously converted to IBF via ester
hydrolysis of BBP, followed by spontaneous oxo bridge formation.
After 7.5 h, the conversion of IBF to other compounds was clearly
differentiated depending on the enzyme used. Apparently, BM
was an ester hydrolysis product of BBP. The production of BMP
and DMP likely occurred via the transesterification reaction
of esterase or cutinase in 0.1% methanol. This is not surprising
because cutinase and esterase have been widely used as biocatalysts
catalyzing esterification and transesterification in organic
solvents (
5,
6,
34). The methyl and butyl esters in BMP and
DMP seem to originate from methanol and one of the hydrolysis
products of BBP, respectively. Except for the unidentified chemical
(X) produced by cutinase, the BBP-derived chemicals (BMP, DMP,
BM, and IBF) are not currently classified as endocrine-disrupting
chemicals associated with effects on the endocrine system in
animals and humans or in vitro (
http://www.kfda.go.kr/webzine/endocrine/endocrine/).

Toxicity estimation of BBP-derived degradation products by using recombinant bioluminescent bacteria.
Toxicity detection using recombinant bioluminescent
E. coli is not directly related to a toxic effect in animals and/or
humans, and it is now generally accepted as a potential method
for environmental monitoring of various industrial wastes and
pollutants, including genotoxicants and stress inducers (
9,
24,
27,
33,
40).
First, general toxicity due to nonspecific cellular stresses was analyzed by using strain GC2. Under increased cellular stress that represses cell growth, the BL emitted by the GC2 strain is subject to being decreased. As shown in Fig. 6a, the final products of degradation by C. cylindracea esterase significantly decreased the relative BL, and therefore, the presence of a toxic component(s) seems evident. Supplementing the bioluminescent culture with BBP (500 ppm) did not decrease the BL (Fig. 6a); hence, BBP did not seem to be toxic to bacterial cells, although endocrine-disrupting chemicals like BBP have been known to potentially interfere with human endogenous hormones (10, 15, 17). As is evident in Fig. 6a, no harmful effect was detected with the enzyme itself, cutinase (100 mg liter-1), or esterase (100 mg liter-1). In the final products of both enzymatic decomposition processes, the amounts of BM and DMP were typically negligible, although they were comparable to the amounts of IBF. Consequently, BMP, a major product of degradation by esterase, seems to be the toxic compound causing the significant cellular stresses.
We investigated which type of cellular damage was related to
BMP toxicity. As shown in Fig.
6b, BBP (500 ppm) and the products
of its degradation by cutinase never caused any cellular damage,
which is consistent with the results shown in Fig.
6a. Figure
6b shows that BMP exerted oxidative damage as well as protein
damage on the bacteria. Cellular stress by oxidative hazards
like active oxygen species may be a great threat to the structures
and functions of proteins, nucleic acids, lipids, and membranes,
whether they are added externally or produced intracellularly.
Also, the increase of BL due to the induction of the
grpE promoter
(a heat shock promoter) indicated that defective protein synthesis
took place in the presence of BMP.
For in situ BBP degradation with cutinase, the addition of the purified cutinase or fungus itself to BBP-contaminated sites does not seem to be practical. A plausible approach to the practical application of cutinase for BBP degradation may be to develop a microbial gene expression system for producing recombinant cutinase. The recombinant yeast system may have a great advantage in that extracellular production of recombinant enzyme is possible, and therefore, the cell-free medium containing a large amount of recombinant cutinase can be applied directly to the in situ degradation of BBP without costly purification.

ACKNOWLEDGMENTS
This work was supported by a Korea University Grant.
We thank Jin-Soo Park and Byoung-Chan Kim at Kwangju Institute of Science and Technology for their technical assistance in the utilization of GC/MS and the bioluminescent bacteria.

FOOTNOTES
* Corresponding author. Mailing address: Department of Chemical and Biological Engineering, Korea University, 1, 5-Ka, Anam-Dong, Sungbuk-ku, Seoul 136-701, South Korea. Phone: 82-2-3290-3304. Fax: 82-2-926-6102. E-mail:
leejw{at}korea.ac.kr.


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Applied and Environmental Microbiology, September 2002, p. 4684-4688, Vol. 68, No. 9
0099-2240/02/$04.00+0 DOI: 10.1128/AEM.68.9.4684-4688.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.