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Applied and Environmental Microbiology, April 2001, p. 1484-1489, Vol. 67, No. 4
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.4.1484-1489.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Seasonal Variation and Indirect Monitoring of
Microcystin Concentrations in Daechung Reservoir, Korea
Hee-Mock
Oh,*
Seog
June
Lee,
Jee-Hwan
Kim,
Hee-Sik
Kim, and
Byung-Dae
Yoon
Environmental Bioresources Laboratory, Korea
Research Institute of Bioscience and Biotechnology, Yusong, Taejon
305-600, Korea
Received 4 October 2000/Accepted 24 January 2001
 |
ABSTRACT |
Physicochemical and biological water quality, including the
microcystin concentration, was investigated from spring to autumn 1999 in the Daechung Reservoir, Korea. The dominant genus in the cyanobacterial blooming season was Microcystis. The
microcystin concentration in particulate form increased dramatically
from August up to a level of 200 ng liter
1 in early
October and thereafter tended to decrease. The microcystin concentration in dissolved form was about 28% of that of the
particulate form. The microcystins detected using a protein phosphatase
(PP) inhibition assay were highly correlated with those microcystins detected by a high-performance liquid chromatograph (r = 0.973; P < 0.01). Therefore, the effectiveness of a
PP inhibition assay for microcystin detection in a high number of water
samples was confirmed as easy, quick, and convenient. The microcystin
concentration was highly correlated with the phytoplankton number
(r = 0.650; P < 0.01) and
chlorophyll-a concentration (r = 0.591;
P < 0.01). When the microcystin concentration
exceeded about 100 ng liter1, the ratio of particulate to
dissolved total nitrogen (TN) or total phosphorus (TP) converged at a
value of 0.6. Furthermore, the microcystin concentration was lower than
50 ng liter1 at a particulate N/P ratio below 8, whereas
the microcystin concentration varied quite substantially from 50 to 240 ng liter1 at a particulate N/P ratio of >8. Therefore,
it seems that the microcystin concentration in water can be estimated
and indirectly monitored by analyzing the following: the phytoplankton
number and chlorophyll-a concentration, the ratio of the
particulate and the dissolved forms of N and P, and the particulate N/P
ratio when the dominant genus is toxigenic Microcystis.
| |
INTRODUCTION |
Blooms of the cyanobacterium
Microcystis aeruginosa are ubiquitous phenomena in eutrophic
lakes and reservoirs in many countries of the world. Many strains of
Microcystis are known to produce cyanobacterial hepatotoxins
called microcystins (MC). These toxins are soluble peptides and are
lethal to many kinds of aquatic organisms (2, 23, 28). MC
are found in strains of the genera Microcystis, Oscillatoria,
Anabaena, and Nostoc (26). To date, at
least 69 MC have been structurally characterized (9).
The Daechung reservoir located in the middle of South Korea was
formed by the construction of a multipurpose dam in 1980 to conserve
water resources for drinking, agricultural, and industrial use
and for electric power supply. Since the end of the 1980s, the
reservoir has shown some eutrophic phenomena, such as cyanobacterial blooms, in the summer and a deterioration in water quality. With the
appearance of cyanobacterial blooms, the production of cyanobacterial toxins, particularly MC, becomes a threat to human health and natural
resources (10, 20, 22). Therefore, the ability to detect
and predict MC in water resources is very important.
Normally, a high-performance liquid chromatography (HPLC)
analysis is used for the detection and qualification of MC in water (7, 8, 9). However, this method has certain weaknesses in
that it usually requires a concentration process and is only feasible
in a laboratory equipped with an HPLC system. Recently, a protein
phosphatase (PP) inhibition assay was introduced for detecting MC in
water and algal samples. The PP inhibition assay for MC consists of
measuring the release of acid-soluble 32P from
32P-labeled glycogen phosphorylase (16) or a
colorimetric assay utilizing the ability of PP-1 to dephosphorylate
p-nitrophenyl phosphate (1, 27). Although some
research has been carried out to compare the results from the HPLC and
PP inhibition assays (30), a clear relationship between
these methods has not yet been established.
MC production by cyanobacteria results from cyanobacterial blooms
caused by an abundance of nutrients and favorable conditions for
cyanobacterial growth. Changing environmental factors in a water system
will have an impact on the MC concentration. Chlorophyll-a would appear to be useful for an initial estimate of a MC concentration in field situations dominated by potentially MC-producing genera (6, 15). The relationships between MC concentration and
the N and P concentrations in water have already been studied
(11, 12, 24, 25, 29). However, the development of proper
parameters, including the ratios of particulate N to P and particulate
to dissolved N or P, to estimate MC concentrations is still needed to
improve the ability to manage water quality.
Accordingly, this study monitored the changes in the MC
concentration in water and algal samples taken every week during the period of cyanobacterial blooms. In addition, methods for detecting MC
were evaluated for ease and convenience, along with an indirect monitoring method for estimating MC concentrations in eutrophic waters.
| |
MATERIALS AND METHODS |
Sampling and field survey.
The Daechung Reservoir is located
on the upper part of the Geum River in the central region of South
Korea. This reservoir is a large branch-type lake with a 72-m-high dam
and a gross storage capacity of 1,490 Mm3. The reservoir is
mainly subject to agricultural runoff. The sampling site was located on
the shore in the vicinity of the Daechung Reservoir dam. The depth of
the sampling site was about 20 m. The sampling was conducted
weekly from the same site from 27 April to 12 October 1999. In total,
the sampling was conducted 25 times from spring to autumn. The water
temperature and Secchi depth of the sampling site were measured with
portable instruments (YSI model 95; Secchi disk). The samples for water
analysis were collected at a depth of 0 to 0.1 m using a Van Dorn
water sampler (WILDCO Instruments) and stored in 20-liter polyethylene
bottles at 4°C until the laboratory analysis was done. The samples
for plankton identification and enumeration were preserved in Lugol's solution.
Physicochemical water quality analysis.
A 500-ml portion of
each water sample was centrifuged for 10 min at 15,000 × g (Sorvall model RC5C). The supernatant was then used to analyze
the levels of dissolved N and P. The pellets, including any
particulate material, were washed with distilled water followed by
centrifugation and stored at 
65°C for further analysis. The
particulate C, which was mainly composed of cellular C, was determined
with a total organic carbon analyzer (Shimadzu model 5000A). The total
N (TN) and P (TP) were determined after persulfate oxidation to nitrate
(3) and orthophosphate (17), respectively.
The nitrate was determined with a Szechrome NB reagent (33), and the orthophosphate was determined by the
phosphomolybdate method (18).
Biological water quality analysis.
Chlorophyll-a
was extracted using a chloroform-methanol mixture (2:1 [vol/vol]) and
measured with a fluorometer (Turner model 450) (31). The
phycocyanin was analyzed using the whole-cell absorption spectrum
method (19). The cell pellet was extracted twice in 80%
acetone and then resuspended in a 0.2 M sodium acetate buffer (pH 5.5).
The absorbance was measured at 625, 678, and 725 nm. The phytoplankton
and zooplankton were enumerated with a hemocytometer (Fuchs-Rosenthal
Ultra Plane; Hausser Scientific) under a phase-contrast microscope
(MICROPHOT-FXA; Nikon).
MC analysis by HPLC.
Algal cells from natural samples were
collected and concentrated using a Whatman GF/C filter. Those filter
papers containing algal cells were lyophilized and stored at 20°C
until the chemical analysis was performed. The analytical procedure, as
previously reported by Harada et al. (8), was as follows.
The lyophilized algal cells were extracted three times with 50 ml of
5% (vol/vol) acetic acid for 30 min. The extract was then centrifuged
at 9,300 × g, and the supernatant was passed through a
C18 cartridge (Sep-Pak; Waters Assoc.). The cartridge
containing MC was first rinsed with 10 ml of water, followed by 10 ml
of 10% (vol/vol) methanol in water. The MC adsorbed on the cartridge
were finally eluted with 10 ml of methanol. The eluate was then
evaporated under reduced pressure below 40°C, and the residue,
dissolved in methanol, was subjected to an HPLC analysis (CLASS-LC10;
Shimadzu). An HPLC equipped with a constant-flow pump was used with a
variable-wavelength UV detector operated at 238 nm. The separation was
performed with a Nucleosil C18 column (5 µm; 150-by
4.6-mm inside diameter) with a mobile-phase, methanol-0.05 M phosphate
buffer (57:43; pH 3.0) at a flow rate of 1.0 ml min1. The
MC were identified based on their UV spectra and retention times
(14) and by spiking the sample with a purified standard of
MC-LR, -RR, and -YR (Sigma, St. Louis, Mo.). In addition, the MC peaks
were isolated and identified according to their mass spectra. The
recoveries of MC-RR and -LR were 93.2% ± 3.1% and 92.7% ± 2.9%
3 h after the MC were spiked within a range of 20 to 200 ng
liter1. Each analysis was performed in triplicate.
MC analysis by PP inhibition assay.
An aliquot (10 ml) of
the natural sample was filtered with a Whatman GF/C filter. The
filtrate was then directly subjected to a PP inhibition assay. The
algal cells were lyophilized, extracted, and purified as described
above. After concentration, the residue was dissolved in 10 ml of
distilled water and subjected to the PP inhibition assay. The PP
activity was determined with some modifications as previously described
by Lambert et al. (13). The 32P-labeled
phosphorylase-a was prepared using a commercial kit from Gibco BRL
(Gaithersburg, Md.). To determine the PP inhibition activity of the
algal cells, 100 ml of each water sample was filtered with a Whatman
GF/C filter. The filter papers were frozen at 70°C, extracted with
5% acetic acid, purified with Sep-Pak cartridges, and then diluted
with a buffer (pH 7.6) containing 20 mM imidazole-HCl, 0.1 mM EDTA, 1 mg liter1 bovine serum albumin and 0.1% (vol/vol)
-mercaptoethanol.
The dephosphorylation was conducted by mixing 20 µl of each water
sample with 20 µl of PP-1 and 20 µl of the 32P-labeled
phosphorylase-a. The samples were then incubated for 30 min at 30°C,
and the reaction was stopped by the addition of 180 µl of 20%
trichloroacetic acid. The samples were kept on ice for 10 min and
centrifuged at 15,000 × g for 3 min, and then the supernatants were collected. The PP activity of the sample was taken as
the radioactivity released in the supernatant as determined by a liquid
scintillation counter (Beckman model 6000A).
MC-RR was used for the preparation of standard curves by PP inhibition
assay, because it was most frequently detected in the
lakes and rivers
of Korea. The inhibition of PP-1 by MC-RR has
been shown to have a
sigmoid response curve when percent activity
of PP-1 is plotted versus
log MC-RR concentrations ranging from
10
8 to
10
11 M. The PP-1 activities of all samples, standard
MC-RR and sample,
were calculated by the equation percent PP-1
activity = 100
[(sample cpm
blank cpm) × 100%/(control cpm
blank cpm)], where
(i) control cpm is the
maximum activity of the PP-1 enzyme (100%
activity without MC-RR) and
(ii) blank cpm is the free [
32P]phosphate in the
phosphorylase-a
solution.
Statistical analysis.
The particulate-to-dissolved TN and TP
ratios as a function of the MC concentrations were curve fitted with
either exponential-decay or exponential-rise equations using SigmaPlot
5.0 software (SPSS Inc., Chicago, Ill.). Repeated measurements for the
variance analysis (P < 0.05) were used to evaluate the
significance of these experimental results.
| |
RESULTS |
Changes in phytoplankton numbers and chlorophyll-a
concentration.
Changes in the phytoplankton density and
chlorophyll-a concentration, as an indicator of algal
biomass, were investigated for 6 months, from April to October 1999, in
the Daechung Reservoir (Fig. 1). The
number of phytoplankton increased dramatically up to 2 × 105 to 3 × 105 ml1 in
August and October. In August, the dominant species were cyanobacteria, which were composed of Microcystis spp. (47%),
Anabaena spp. (39%), and Oscillatoria spp.
(6%). In October, the phytoplankton numbers were still high, but the
dominant species changed to diatoms.
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FIG. 1.
Number of phytoplankton and cyanobacteria (top) and
chlorophyll-a concentration and water temperature (bottom)
in Daechung Reservoir. Sampling was carried out at 1-week intervals
from 27 April to 12 October 1999. The error bars indicate standard
deviation (n = 3).
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|
The chlorophyll-
a concentration varied within a range of 3 to 24 µg liter
1 and reflected the number of
phytoplankton. The maximum chlorophyll-
a concentration was
recorded at 24 µg liter
1 on August 31 and was
concomitant with a cyanobacterial number
of 2.5 × 10
5
ml
1. The water temperature, which is an important factor
in supporting
algal growth, varied from 19°C in the spring to 31°C
in the summer
and gradually decreased in the
autumn.
Seasonal variation of MC concentration.
The MC concentrations
in water and algal samples were analyzed by a PP inhibition assay. The
variation in the MC concentrations in the dissolved and particulate
samples is shown in Fig. 2. Measurable MC
levels were detected in dissolved and particulate fractions in all the
examined samples. In particular, from the beginning of August, the
particulate MC concentration increased dramatically up to a level of
200 ng liter1 in the beginning of October; thereafter, it
tended to decrease, judging from the measurements of not only MC
concentration but also cyanobacterial numbers, chlorophyll-a
concentration, and water temperature. The particulate MC were highly
correlated with the dissolved MC in the water body (Y = 5.88X 24.90; r = 0.891; P < 0.01). The
dissolved MC composed about 28% of the particulate form.
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FIG. 2.
MC concentration of particulate and dissolved forms in
Daechung Reservoir. Sampling was carried out at 1-week intervals from
27 April to 12 October 1999. The error bars indicate standard deviation
(n = 3).
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|
MC analysis by HPLC has low sensitivity. Therefore, the HPLC method is
normally used for relatively high concentrations of
MC; otherwise, it
is necessary to concentrate a water sample to
the detectable level for
MC. The water samples collected between
August and October contained
sufficient MC to be analyzed by HPLC.
MC concentrations analyzed using
HPLC were compared with the results
of the PP inhibition assay (Fig.
3). The MC were composed of MC-LR
and
-RR. MC-RR was the main component, and MC-YR was not detected
at all.
The MC concentrations detected by the PP inhibition assay
were highly
correlated with those determined by HPLC (
Y = 3.28
X 84.87;
r = 0.973;
P < 0.01). However, the MC
concentrations
measured by the HPLC method were only about 70% of
those measured
by the PP inhibition assay.
Relationship between MC concentration and algal biomass, water
quality, and zooplankton numbers.
Certain physicochemical and
biological indicators of water quality that appeared to be related to
the MC concentration were analyzed for their statistical relationships
(Table 1). The total MC concentration was
highly correlated with the chlorophyll-a concentration
(r = 0.591; P < 0.01) and phytoplankton density (r = 0.650; P < 0.01). The chlorophyll-a
concentration was highly correlated with the number of phytoplankton,
cyanobacteria, and Microcystis (P < 0.01)
and Anabaena (P < 0.05) organisms.
The standing crops of zooplankton were within a range of 7 individuals
liter
1 on May 25 to 390 individuals liter
1
on October 12 and showed a mean value of 93 individuals
liter
1 over the period of investigation. The dominant
species of zooplankton
were
Tintinnopsis cratera, Polyarthra
trigla, and
Cyclops strenuus.
The number of zooplankton
as primary consumers in an aquatic ecosystem
was correlated with the
chlorophyll-
a concentration and also the
phycocyanin
concentration. The phycocyanin concentration showed
a high correlation
with the number of cyanobacteria and
Microcystis and
Anabaena organisms.
The Secchi depth, as an easy way to determine the trophic status of a
body of water, was within a range of 2.3 m on August
3 to 6.5 m on May 18. The Secchi depth was negatively correlated
with all the
other water qualities examined, which were either
directly or
indirectly related with the algal biomass. In particular,
the Secchi
depth was highly negatively correlated with the
chlorophyll-
a concentration, phytoplankton density, and
particulate
C.
Relationship between MC concentrations and nutrients.
The
ratio of particulate to dissolved TP or TN was expressed as a function
of the MC concentration in water (Fig.
4). In the case of TP, the ratio of
particulate to dissolved TP decreased dramatically with increasing MC
concentration up to about 100 ng of MC liter1.
Interestingly, when the MC concentration exceeded about 100 ng
liter1, the ratio of particulate to dissolved TP
converged at a value of 0.6.
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FIG. 4.
Relationship between MC concentration and
particulate-to-dissolved TP and TN in Daechung Reservoir.
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In contrast, the ratio of particulate to dissolved TN increased with
increasing MC concentration up to about 100 ng of MC
liter
1. When the MC concentration exceeded about 100 ng
liter
1, the ratio of particulate to dissolved TN
converged at a value
of 0.6. Therefore, it would appear that the ratio
of particulate
to dissolved N or P at 0.6 is the threshold value for
determining
high or low MC concentration. In other words, the MC
concentration
was lower than 100 ng liter
1 when the ratio
of particulate to dissolved TP was high while
the
particulate-to-dissolved TN ratio was
low.
The N/P atomic ratio in particulate form, which was mainly composed of
phytoplankton, varied within a range of 4 to 12 in
this body of water
(Fig.
5). The MC concentration in the
water
varied with the particulate N/P ratio. That is, at a particulate
N/P ratio under 8, the MC concentration was lower than 50 ng
liter
1, whereas at a particulate N/P ratio of >8, the MC
concentration
varied quite substantially, from 50 to 240 ng
liter
1. In other words, the level of the MC concentration
was also determined
to some extent by the particulate N/P ratio.
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FIG. 5.
MC concentration as a function of particulate N/P atomic
ratio in total (dissolved plus particulate) and particulate form in
Daechung Reservoir.
|
|
The change of MC in particulate and total forms relative to the N/P
ratio also showed a similar pattern. Consequently, an
increase in the N
concentration in the cells exhibited a potential
increase in the MC
concentration in the cells and also in the
body of
water.
| |
DISCUSSION |
Trophic state of Daechung Reservoir.
According to Organization
for Economic Cooperation and Development guidelines (21),
8 µg of chlorophyll liter1 is considered the boundary
between mesotrophy and eutrophy. The chlorophyll-a
concentration exceeded 8 µg liter1 with a frequency of
56% (14 out of the 25) in the samples examined. The
chlorophyll-a concentrations in the samples taken in August, September, and October, except for one sample, were particularly high,
within a range of 12 to 24 µg liter1. From these
results, it would appear that the Daechung Reservoir is in a eutrophic
state and that this phenomenon is severe in summer and early autumn.
The maximum chlorophyll-
a concentration was recorded at 24 µg liter
1 on August 31 and was concomitant with an
increase in cyanobacterial
numbers (Fig.
1). That is, the
chlorophyll-
a concentration was
highly correlated with
phytoplankton numbers (
r = 0.699;
P < 0.01)
and
cyanobacterial numbers (
r = 0.611;
P < 0.01)
(Table
1). Therefore,
it can be concluded that the
chlorophyll-
a concentration in the
Daechung reservoir is
mainly determined by the number of cyanobacteria
in the
phytoplankton.
Variation of MC concentration.
After August, the MC
concentration in particulate form increased dramatically, up to 200 ng
liter1, while the dissolved MC did not vary much (Fig.
2). Water safety guidelines have been proposed with 1 µg of
cyanobacterial peptide toxins liter1 as the maximum
concentration in drinking water (4). Recently, this
guideline was also proposed by the World Health Organization (32). Therefore, it would appear that the MC concentration
in the Daechung Reservoir is much lower than the level that would cause
concern. In a previous report (10), MC-RR was identified as the main component of MC variants in Korean reservoirs, and the
total content of MC varied from 288 to 2,612 µg g1,
which corresponds to a concentration per water volume of 0.4 to 21.6 µg liter1.
The MC concentrations in dissolved form were about 28% of those in
particulate form. In related research, the high percentage
of
extracellular MC in filtered lake water (>20%) at the end of
the
bloom period would seem to suggest that the release of MC
occurs during
the senescence and decomposition periods of
Microcystis cells (
22). Dissolved MC have seldom been detected in
water
during cyanobacterial blooms, and if detected, the concentrations
have been very low compared to the toxins in the particulate matter
(
12). In particular, in the season of severe
cyanobacterial
blooms, most MC were in particulate form (Fig.
2). Based
on these
results, the removal of particles, including algal cells, from
water resources is recommended to effectively reduce the risk
of MC in
drinking
water.
Comparison of methods for MC analysis.
The MC concentrations
detected by the PP inhibition assay were highly correlated with those
detected by HPLC (Fig. 3). Similarly, in other research, the MC content
of field samples from German lakes estimated on the basis of a PP-1
inhibition assay was compared to that obtained by a reversed-phase
HPLC, and a good correlation was observed (r = 0.9202;
P < 0.0001) (30). Therefore, it is apparent
that a PP inhibition assay is a quick, easy, and convenient method to
use when screening many water samples for MC. For example, about 300 samples can be analyzed within a day. In contrast, the HPLC assay is
also needed to gain more quantitative and qualitative information on
the MC in the water body.
The MC concentrations detected by the PP inhibition assay were about
1.4 times higher than those detected by HPLC. This is
the opposite of
the result of Wirsing et al. (
30), who reported
that the
colorimetric PP-1 assay has a tendency to slightly underestimate
the MC
content in cyanobacterial samples compared with the reversed-phase
HPLC
results. In contrast, the hepatotoxicity measured in rat
bioassays by
other investigators (
5) was usually two to three
times
higher than the maximal toxicity predicted from their MC
contents. It
is also probable that other substances in either
the algae or their
environment may cause reactions that are synergistic
with or additive
to
MC.
In this study, MC were detected in all the samples examined from spring
to autumn. There are two possibile reasons for this
phenomenon. First,
MC-producing cyanobacteria existed in all the
examined samples during
the survey period and produced MC. Second,
due to an unknown factor,
the PP inhibition analysis used in this
work overestimated the MC
content in the water and
cells.
Indirect monitoring of MC.
MC analysis is a necessary process
to determine the safety of drinking water and water resources; however,
it is a somewhat complex process when using an HPLC or isotopes and
requires much time. Therefore, there is current interest in the
development of a simpler and more convenient method for estimating the
MC concentration in water. After this process, further analysis with an
HPLC or isotopes can be carried out with selected samples to gain more
detailed information. This strategy would seem to be more profitable
for field samples.
MC production by cyanobacteria during blooms is likely related to the
abundance of nutrients and favorable conditions for
cyanobacterial
growth. Changes in the environmental factors in
a water system will
have an impact on the composition of both
the algal species and the
cellular components. As a result, the
MC concentration will also change
relative to the water quality,
nutrient distribution, and cellular
components.
First of all, the MC concentration was highly correlated with
phytoplankton numbers (
r = 0.650;
P < 0.01) and
chlorophyll-
a concentration (
r = 0.591;
P < 0.01). Similarly, in other research,
the seasonal changes in the
MC-LR concentrations were found to
be positively correlated to the
abundance and biomass of the cyanobacterium
Microcystis
aeruginosa, the total and total dissolved P concentrations,
the
pH, and chlorophyll-
a (
11). Therefore, it would
seem plausible
that an initial estimation of the existence of MC based
on phytoplankton
numbers and the chlorophyll-
a concentration
can be used to evaluate
the quality of water for
drinking.
The MC concentrations at a higher ratio (>0.6) of particulate to
dissolved TP were lower than 100 ng liter
1.
Interestingly, where the MC concentrations exceeded about 100
ng
liter
1, the ratio of particulate to dissolved TN or TP
converged at
a value of 0.6. Rapala and Sivonen (
24) also
suggested that
the concentrations of dissolved inorganic N and P may
regulate
the species and strain composition and, hence, the toxicity of
a bloom. Rapala et al. (
25) suggested that MC
concentrations
in different cyanobacterial genera respond similarly to
extracellular
P concentrations: not only cyanobacterial growth but also
the
amounts of intracellular hepatotoxins increase with the P
concentration.
The most significant discriminating factors between the
different
types of blooms were the concentrations of dissolved
PO
4-P and
NO
3-N (
24). The
hepatotoxic
Microcystis blooms exhibited the
highest
concentrations of PO
4-P.
In addition, the MC concentration in the water varied with the
particulate N/P ratio. That is, at a particulate N/P ratio
under 8, the
MC concentration was lower than 50 ng liter
1, whereas at
a particulate N/P ratio of >8, the MC concentration
varied quite
substantially, from 50 ng to 240 ng liter
1. The amount of
toxin in the particulate material correlated positively
with the
cyanobacterial biomass as well as with the TN and TP
concentrations in
the water (
12). In other words, the level
of the MC
concentration was also determined to some extent by
the particulate N/P
ratio.
It is very important to monitor the water quality of lakes and
reservoirs that are sources for drinking water. The toxin microcystin
comes from cyanobacteria and is dominant in an environment where
cyanobacteria grow well. Therefore, the basic water quality must
be
routinely examined to provide data so that analyses of the
presence and
concentration of MC can be conducted, thereby providing
information on
water safety. In order to gain more detailed, accurate
information on
the kinds and concentrations of toxins present,
a further analysis of
MC by using an HPLC assay should be conducted
with selected samples
identified as containing particularly high
toxin
concentrations.
| |
ACKNOWLEDGMENTS |
This work was supported by the Korean Ministry of Science and
Technology (MOST).
We are also grateful to anonymous reviewers for their valuable comments
on this study and to Lorne Hwang for her careful reading of the manuscript.
| |
FOOTNOTES |
*
Corresponding author. Mailing address: Environmental
Bioresources Laboratory, Korea Research Institute of Bioscience and
Biotechnology, P.O. Box 115, Yusong, Taejon 305-600, Korea. Phone:
82-42-860-4321. Fax: 82-42-860-4598. E-mail:
heemock{at}mail.kribb.re.kr.
| |
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Applied and Environmental Microbiology, April 2001, p. 1484-1489, Vol. 67, No. 4
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.4.1484-1489.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
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Abstract
Introduction
