Biotransformation of some monoterpenoid ketones by chlorella vulgaris MCCS 012

Article abstract of DOI:10.1007/s10600-010-9728-9

Biotransformation of several monoterpene ketones, including carvone, pulegone, piperitone, menthone, and fenchone, was carried out by the locally isolated unicellular microalgae Chlorella vulgaris. The microalgal strain was isolated during a screening program from soil samples collected from paddy-fields of Fars Province, in the south of Iran. Chlorella vulgaris was cultured in 250 mL conical flasks, each containing 50 mL of BG-11 liquid medium and 20μL levels of terpene substrates, incubated at a temperature of 28±2°C and illuminated continuously with fluorescent lamps with shaking at 80 rpm. The metabolites were identified by thin-layer chromatography and GC-MS. Chlorella vulgaris has the ability to reduce the C=C double bond of carvone to yield trans-dihydrocarvone and cis-dihydrocarvone. The cell line reduced menthone and pulegone to the same product and gave menthol. Study of Chlorella vulgaris with substrates of piperitone and fenchone showed no reaction in these substrates. Chlorella vulgaris MCCS 012 was assigned according to the 18S rRNA gene sequence. The DNA sequence of the 18S rRNA gene of Chlorella vulgaris MCCS 012 was recorded in the NCBI under the accession number EU374170.

Full text of DOI:10.1007/s10600-010-9728-9

Chemistry of Natural Compounds, Vol. 46, No. 5, 2010
BIOTRANSFORMATION OF SOME MONOTERPENOID
KETONES BY Chlorella vulgaris MCCS 012
Younes Ghasemi,* Abdolali Mohagheghzadeh, Zahra Ostovan,
Maryam Moshavash, Sara Rasoul-Amini,
UDC 547.596
and Mohammad Hossein Morowvat
Biotransformation of several monoterpene ketones, including carvone, pulegone, piperitone, menthone,
and fenchone, was carried out by the locally isolated unicellular microalgae Chlorella vulgaris. The microalgal
strain was isolated during a screening program from soil samples collected from paddy-fields of Fars Province,
in the south of Iran. Chlorella vulgaris was cultured in 250 mL conical flasks, each containing 50 mL of
BG-11 liquid medium and 20 ꢀL levels of terpene substrates, incubated at a temperature of 28ꢁ2ꢂC and
illuminated continuously with fluorescent lamps with shaking at 80 rpm. The metabolites were identified by
thin-layer chromatography and GC-MS. Chlorella vulgaris has the ability to reduce the C=C double bond of
carvone to yield trans-dihydrocarvone and cis-dihydrocarvone. The cell line reduced menthone and pulegone
to the same product and gave menthol. Study of Chlorella vulgaris with substrates of piperitone and fenchone
showed no reaction in these substrates. Chlorella vulgaris MCCS 012 was assigned according to the 18S
rRNA gene sequence. The DNA sequence of the 18S rRNAgene of Chlorella vulgaris MCCS 012 was recorded
in the NCBI under the accession number EU374170.
Keywords: biotransformation, monoterpene, microalgae, Chlorella vulgaris.
Biotransformation has been extensively applied in the fermentation industry, for example, in the production of steroids.
In the course of our work related to the biotransformation of exogenous steroid microalgae, we investigated the bioconversion
of some monoterpenoid ketones by Chlorella vulgaris MCCS 012. [1–4]. Monoterpenes are natural substances that present a
small carbon pool with a high turnover rate in the annual global carbon cycle [5]. The amount of volatile monoterpenes emitted
14
from trees is estimated to be 127 ꢃ 10 g of carbon/year [6]. The low price and simple structure of monoterpenes such as
carvone, pulegone, and menthone make them ideal targets for bioconversion by microorganisms to yield commercially important
products [7]. Commercially useful chemical building blocks and pharmaceutical stereoisomers can also be produced by
bioconversion of monoterpenes. Products produced by bioconversion processes may be considered as natural [8]. Only a few
studies have been reported on the biotransformation of monoterpenes by Chlorella species. One study cites the biotransformation
of carvone and menthone by the microalga Chlorella minutissim [9]. Preliminary taxonomical studies show that Chlorella
vulgaris is common in the paddy-fields of Fars Province located in the south of Iran, beside microalgae like Oocystis,
Scenedesmus, and some unicellular and filamentous cyanobacteria [1]. In this study, the biotransformation of carvone, pulegone,
piperitone, menthone, and fenchone as an exogenous substrate was carried out by a locally isolated strain of a unicellular
microalga Chlorella vulgaris. Until today, Chlorella vulgaris has not been examined in the transformation of monoterpenes.
The aim of this study is to identify the ability of locally isolated Chlorella vulgaris to convert monoterpenoid ketones as an
exogenous substrate. The strain was recognized by morphological characterization and assigned according to the 18S rRNA
gene sequence. The isolated alga was classified by the Microalgal Culture Collection of Shiraz University of Medical Sciences,
Faculty of Pharmacy, Shiraz, Iran, as a strain of Chlorella vulgaris MCCS 012. The partial sequence of the 18S rRNA gene of
Chlorella vulgaris MCCS 012 is as follows:
Department of Pharmaceutical Biotechnology and Pharmaceutical Sciences Research Center, School of Pharmacy,
Shiraz University of Medical Sciences, Shiraz, Iran, fax: +98 71 12 42 60 70, e-mail: ghasemiy@sums.ac.ir. Published in
Khimiya Prirodnykh Soedinenii, No. 5, pp. 619–621, September–October, 2010. Original article submitted March 30,
2009.
734
0009-3130/10/4605-0734 02010 Springer Science+Business Media, Inc.

1
gcatttgcca
aggatgtttt
tagtctcaac
cggcacctta tgagaaatca
cattaatcaa
cataaacgat
gaacgaaagt tgggggctcg aagacgatta
gccgactagg gatcggcgga tgtttcttcg
61 gataccgtcc
121 atgactccgc
aagtttttgg
gttccggggg gagtatggtc
181 gcaaggctga aacttaaagg aattgacgga agggcaccac caggcgtgga gcctgcggct
241 taatttgact
301 agagctcttt
361 ttgtcaggtt
caacacggga aaacttacca
ggtccagaca tagtgaggat tgacagattg
cttgattcta
tgggtggtgg tgcatggccg ttcttagttg gtgggttgcc
gattccggta
acgaacgaga cctcagcctg ctaaatagtc
acggttggtt
421 cgccagccgg cggacttctt
481 ataacaggtc tgtgatgccc
541 caacgagcct agccttggcc gagaggcccg ggtaatcttc
601 atagattatt gcaattattaa
agagggacta ttggcgacta
gccaatggaa gcatgaggca
ttagatgttc
tgggccgcac gcgcgctaca ctgatgcatt
gaaactgcat cgtgatgggg
The DNA sequence of 18S rRNA gene of Chlorella vulgaris MCCS 012 was recorded in the NCBI under the
accession number EU374170. The result of PCR blasted with other sequenced microalgae in NCBI showed 100% homology
to the 18S small subunit rRNA of other strains of Chlorella vulgaris.
Initially, the optimal growth patterns of Chlorella vulgaris were established. The growth was determined by direct
counting and absorbance at 680 nm. Monoterpene substrates were then added to the cell cultures in the logarithmic phase of
6
–1
growth (2.8–3.0 ꢃ 10 cells mL ). After 24 hours incubation, Chlorella vulgaris MCCS 012 reduced the C=C double bond of
(+)-carvone (1) to yield trans-dihydrocarvone (6) and cis-dihydrocarvone (7). The microalga reduced both (–)-menthone (2)
and (+)-pulegone (3) to dl-menthol (8). In this study Chlorella vulgaris did not react with (–)-fenchone (4) and (–)-piperitone
(5). The chemical structures of the substrates and the products that underwent biotransformation by Chlorella vulgaris are
shown in Fig. 1.
O
O
O
+
1
6
7
O
O
O
O
OH
5
4
2
8
3
Fig. 1. Chemical structures of the substrates and the products biotransformed by Chlorella vulgaris.
Microalgae are photoautotrophic and, therefore, do not require an organic substrate for energy. Consequently, the
culture of microalgae is simpler and cheaper than that of bacteria, yeasts, or fungi. They are easily and quickly cultured in an
inexpensive medium containing simple salts, which decreases the probability of contamination by other microorganisms. This
is an important advantage when considering the potential of microalgae in the biotransformation of readily available chemicals
such as carvone and menthone into compounds with a higher economic value in the food and perfume industries.
In this study, various monoterpenes, including carvone, pulegone, piperitone, menthone, and fenchone, were chosen
for biotransformation evaluation. Using these compounds, we examined the biotransformation of monoterpenoids in a cell
culture of Chlorella vulgaris to elucidate the metabolic behavior of the green algal cells at a concentration of ca. 100 ppm.
Both carvone and piperitone are unsaturated ketones. (+)-Carvone was reduced to trans-dihydrocarvone and cis-dihydrocarvone.
No biotransformation of (–)-piperitone was observed. It is possible that the position of the methyl and isopropyl groups in
carvone and piperitone relative to the carbonyls determines the orientation and the fitness of the molecules in the catalytic sites
of the reductase involved. In fungi, enoate reductases are responsible for the reduction of activated C=C bonds. The enzymes
responsible for the reduction of carvone are apparently present in many yeasts, fungi, plants, and algae [10]. Methylethenyl
group reduction and hydroxylated derivatives were not found in the metabolism of carvone by Chlorella vulgaris.
735

Dihydrocarvone and neodihydrocarveol were found in the biotransformation of (–)-carvone by four species of microalgae,
Nannochloris, Dunaliella, Porphyridium, and Isochrysis [9]. They found an initial reduction of the ꢄ,ꢅ-unsaturated double
bond, followed by the carbonyl group in carvone, leaving the exocyclic C=C bond of the 1-methylethenyl group unaffected
[9]. It is interesting to note that Chlorella vulgaris reduced the carbonyl group and the exocyclic C=C bond of the 1-methylethenyl
group in (+)-pulegone to give menthol. Van Dyk s group [10] showed that the black yeast Hormonema sp. could transform
(+)-pulegone to neomenthol. Alcohol dehydrogenases are involved in the reduction of carbonyl groups and are responsible for
the formation of S-alcohols from (–)-menthone and (+)-pulegone following Prelog s rule. Dehydrogenases following Prelog s
rule are apparently more abundant [10]. Reduction of the unconjugated carbonyl group of (–)-menthone by Chlorella vulgaris
gave menthol. This result is similar to findings observed in the biotransformation of (–)-menthone by Chlorella minutissim [9].
During the biotransformation of foreign substrates by Chlorella vulgaris, the cells showed similar metabolic behaviors, resulting
in reduction, on the structure of the substrate added. In recent years, bioconversion yields and production technology have
both improved, which suggests that the production of many economically viable terpenoid compounds will be possible in the
future [8]. To the best of our knowledge, no research has been conducted on the biotransformation of monoterpenes by
Chlorella vulgaris. As these results show, this microalga might be considered as a useful biocatalyst for some types of
monoterpenes.
EXPERIMENTAL
Chemical Compounds. (+)-Carvone (1), (–)-menthone (2), and (+)-pulegone (3) were purchased from Merck.
(–)-Fenchone (4) and other reagents were from Sigma and Fluka. (–)-Piperitone (5) was kindly provided by Dr.A. R. Shahverdi
(Department of Pharmaceutical Biotechnology, Faculty of Pharmacy, Tehran University of Medical Sciences).
Collection, Preservation, and Identification of the Alga. The microalga was isolated, during a screening program,
from soil samples collected from the paddy-fields of Shiraz located in southern Iran (Fars Province) from April to December
2004. Primary culturing was carried out in BG-11 medium [3]. After colonization, pure cultures of living specimens were
prepared using subculturing and the agar plate method in BG-11 medium [11]. Preserved specimens were prepared and the
living specimens were incubated in 50 mL-conical flasks, under constant illumination. Identification of the alga was carried
out using appropriate manuals [12, 13].
18S Ribosomal RNA sequencing: for this purpose, DNA content was first extracted from the Chlorella vulgaris and
then PCR was applied using two set primers. The sequences were amplified using the primers
5 -GTCAGAGGTGAAATTCTTGGATTTA-3 as forward and 5 -AGGGCAGGGACGTAATCAACG-3 as reverse, which
amplify a ~600-bp region of the 18S rRNA gene. PCR products were electrophoresed in a 1% (w/v) agarose gel using TBE
buffer containing 1 ꢀg/mL ethidium bromide. A single ~600-bp band of DNA was cut and extracted from the gel using the
Core Bio Gel Extraction Kit. The sequence was determined by the CinnaGen Company with the primers. Sequence similarity
searches were done with BLAST through the databases of NCBI and the software GeneDoc.
Biotransformation. The fermentation experiments were conducted in 250 mL conical flasks, each containing 50 mL
of BG-11 liquid media. A fresh culture of Chlorella vulgaris was used as inocula at a final cell density of approximately
6
–1
2.8–3.0 ꢃ 10 cells mL . Cell cultures were fed with 5 ꢀL of monoterpene substrates in triplicate and incubated as described
earlier. After 24 hours (analysis time), the cultures were sampled and the samples extracted with dichloromethane for 2 min
and centrifuged. The dichloromethane extract for each analysis was reduced under nitrogen gas to 100 ꢀL prior to TLC and
GC/MS-analysis. For each substrate, control experiments were also carried out, where a sterilized conical flask containing
50 mL of medium was fed with standard samples, and after incubation the cells were analyzed by GC/MS. Furthermore, the
dichloromethane extracts containing the cells were examined by GC/MS to determine the presence of monoterpenes in
non-transformed cells.
From (+)-carvone we obtained trans-dihydrocarvone and cis-dihydrocarvone with 68 and 15% yield, and from
(–)-menthone and (+)-pulegone we obtained menthol with 43 and 38% yield, respectively.
–1
Growth Determination. Cell density (number of cells mL ) was determined by linear absorbance at 680 nm and
direct counting using a light microscope with a 0.1 mm deep counting chamber (Neubauer haemocytomer).
Thin Layer Chromatography. Qualitative analysis of the reaction products was carried out by TLC on a 0.25 mm
thick layer of silica gel G (Kieselgel 60 HF
, Merck). The TLC solvent system was n-hexane–diethyl ether (1:1, v/v),
254+366
and the spots were visualized by iodine vapor and spraying of the plates with a mixture of vanillin–sulfuric acid (6:1, v/v) and
heating in an oven at 100ꢂC for 3 min until color development. The compounds were also visualized under a UV lamp at 254 nm.
736

The qualitative identification was based on the R values of the investigated compounds and the color of the detected compounds
f
during TLC. Control flasks were also extracted using the same procedure as described above and analyzed by TLC [8].
GC/MS Analysis. The GC/MS analyses were carried out using a Hewlett-Packard 6890. The gas chromatograph was
equipped with an HP-5MS capillary column (phenyl methyl siloxane, 25 m ꢃ 0.25 mm i.d.). The oven temperature was
increased from 60ꢂC to 200ꢂC at the rate of 3ꢂC/min and finally maintained at 200ꢂC for 5 min. The carrier gas was helium at
a flow rate of 1 mL/min, and the volume injected was 1 ꢀL of the concentrated samples. The mass spectrometer was operated
in EI mode at 70 eV. The interface temperature was 250ꢂC, and the mass range was 30–600 m/z. The compounds were
identified by comparing the retention indices of the peaks on the HP-5MS column with literature values, computer matching
to the Wiley 275 Library, mass spectral database, and comparing the fragmentation patterns of the mass spectra with those
reported in the literature [14]. Relative percentage amounts of the separated compounds were calculated from total ion
chromatograms by the computerized integrator [15].
ACKNOWLEDGMENT
This work was supported by a grant from the Research Council of Shiraz University of Medical Sciences, Shiraz
University of Medical Sciences, Shiraz, Iran.
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