Effects of Modification of Light Parameters on the Production of Cryptophycin, Cyanotoxin with Potent Anticancer Activity, in Nostoc sp.

Cryptophycin-1 is a cyanotoxin produced by filamentous cyanobacteria. It has been evaluated as an anticancer agent with great potential. However, its synthesis provides insufficient yield for industrial use. An alternative solution for metabolite efficient production is to stress cyanobacteria by modifying the environmental conditions of the culture (Nostoc sp. ATCC 53789). Here, we examined the effects of light photoperiod, wavelength, and intensity. In light photoperiod, photoperiods 24:0 and 16:8 (light:dark) were tested while in wavelength, orange-red light was compared with blue. Medium, high, and very high light intensity experiments were performed to test the effect of light stress. For a 10-day period, growth was measured, metabolite concentration was calculated through HPLC, and the related curves were drawn. The differentiation of light wavelength had a major effect on the culture, as orange-red filter contributed to noticeable increase in both growth and doubled the cyanotoxin concentration in comparison to blue light. Remarkably, constant light provides higher cryptophycin yield, but slightly lower growth rate. Lastly, the microorganism prefers medium light intensities for both growth and metabolite expression. The combination of these optimal conditions would contribute to the further exploitation of cryptophycin.

Improvement of Vip3Aa16 Toxin Production and Efficiency Through Nitrous Acid and UV Mutagenesis of Bacillus thuringiensis (Bacillales: Bacillaceae).

Bacillus thuringiensis Berliner (Bacillales: Bacillaceae) strain BUPM95 was known by the efficiency of its vegetative insecticidal protein (Vip3Aa16) against different Lepidoptera such as Spodoptera littoralis (Lepidoptera: Noctuidae). To overcome the problem of the low quantities of Vip3 proteins secreted by B. thuringiensis strains in the culture supernatant, classical mutagenesis of vegetative cells of BUPM95 strain was operated using nitrous acid and UV rays. The survivors were screened on the basis of their hemolytic activity and classified in three groups: unaffected, overproducing, and hypo-producing mutants. Using different mutants improved in their hemolytic activity, the supernatants showed an improved toxicity toward S. littoralis larvae (83.33-100% of mortality) compared with the wild-type supernatant (76%). After Vip3 protein quantification in the different supernatants, bioassays against S. littoralis larvae demonstrated that mutants M62, M43, and M76 were improved in the efficiency of their toxin as demonstrated by the lower values of LC50 and LC90 compared with the wild-type Vip3Aa16 protein. However, M26 and M73 mutants were improved in the toxin quantities produced in the supernatant. The improvement of the production and the efficiency of B. thuringiensis Vip3 toxins should contribute to a significant reduction of the production costs of these very interesting B. thuringineis proteins and facilitate the use of these toxins in the pest control management.

Influence of Cooking (Microwaving and Broiling) on Cylindrospermopsin Concentration in Muscle of Nile Tilapia (Oreochromis niloticus) and Characterization of Decomposition Products.

Cylindrospermopsin (CYN) has become increasingly important as a freshwater algal toxin, showing cytotoxic effects. This toxin is able to bioaccumulate in freshwater food webs, representing a serious human health problem. Normally, fish is cooked before consumption, and CYN concentration can be altered. For the first time, the effects of microwaving and broiling for 1 and 2 min on CYN concentration and its decomposition products in fish muscle (Oreochromis niloticus) contaminated in the laboratory were investigated, using UPLC-MS/MS and Orbitrap. The results show that cooking the fish reduced unconjugated CYN levels by 11, 10 and 15% after microwaving for 1 and 2 min, and broiling for 2 min, respectively, compared to control fish. Different CYN decomposition products with m/z 416.1234 (7-epi-CYN) and m/z 336.16663 (diasteroisomers C-3A, C-3C, C-3D, C-3E, C-3F) are generated in fish samples submitted to cooking. Based on the relative abundance of the decomposition products, the possible degradation pathways taking place by microwaving may be through the formation of 7-epi-CYN and m/z 336.16663 compounds, whereas in the case of broiling the last route is the only one observed in this study. The influence of cooking and the toxicity characterization of the degradation products generated in CYN-contaminated fish are of importance for more realistic risk evaluation related to their consumption.

Maintenance of residual activity of Bt toxin by using natural and synthetic dyes: a novel approach for sustainable mosquito vector control.

Mosquito control protein from Bacillus thuringiensis gets inactivated with exposure to sunlight. To address this issue, the potential of synthetic and natural dye was investigated as sunlight protectants. Bt SV2 in absence of dyes when exposed to sunlight showed reduced effectiveness against the fourth instars of mosquito larvae. Whereas acriflavin, congo red and violacein were able to maintain 86.4%, 91.6% and 82.2% mosquito larvicidal efficacy of Bt SV2 against IVth instars larvae of Anopheles stephensi Meigen after exposure to sunlight. Similarly, beetroot dye, acriflavin, congo red and violacein maintained 98.4%, 97.1%, 90.8% and 70.7% larvicidal activities against Aedes aegypti Linnaeus after sunlight exposure. Prodigiosin was found to be the best photo-protectant by simultaneously protecting and enhancing Bt activity by 6.16% and 22.16% against A. stephensi and A. aegypti, respectively. Combination of dyes with Bt formulations can be a good strategy for mosquito control programmes in tropical and sub-tropical regions.

Efficacy of olive mill wastewater for protecting Bacillus thuringiensis formulation from UV radiations.

The effectiveness of 10 low-cost UV-absorbers in protecting Bacillus thuringiensis subsp. kurstaki BLB1 toxins against inactivation by UV-A and UV-B irradiation was evaluated in this study. Among them, two by-products, molasses and olive mill wastewater (OMW) were selected for further studies. They were tested at different concentrations of 0.05, 0.1, 0.15 and 0.2% using the para-aminobenzoic acid (PABA) as a common UV protectant. Interestingly, addition of PABA and OMW to BLB1 formulations was found to be most effective in protecting BLB1 spores at 90.8 and 76.4% respectively and in preserving delta-endotoxin concentration at a level of 81.7 and 72.2%, respectively when used at a concentration of 0.2%. The lowest preserved spores (46.3%) and delta-endotoxin level (12.4%) was found using molasses. In contrast, spore count and delta-endotoxin concentration were completely reduced after an exposure of unprotected Bt strain BLB1 to UV radiations up to 96h. SDS-PAGE analysis of protected and unprotected samples revealed that delta-endotoxin bands (130, 65-70kDa) were conserved until 96h of UV exposure in presence of PABA or OMW compared with their disappearance in presence of molasses after 72h of exposure and their dramatically decline from 8h of exposure in unprotected mixture. A complete loss of larvicidal toxicity against Ephestia kuehniella was found after 24h of exposure in absence of any UV-absorber. Addition of OMW or PABA offered the highest levels of insecticidal activity with 63.2 and 74.7% of residual toxicity, respectively. Whereas, molasses addition, as UV protectant retained only 26.3% of residual activity after 96h of exposure. Therefore, addition of OMW by-product to Bt formulation may be a suitable alternative to others synthetic chemical compounds. OMW may also provided added value, be environmentally friendly and less hazardous, when used at low concentration.

Kinetics and mechanisms of cylindrospermopsin destruction by sulfate radical-based advanced oxidation processes.

Cylindrospermopsin (CYN) is a potent cyanobacterial toxin frequently found in water bodies worldwide raising concerns over the safety of drinking and recreational waters. A number of technologies have been investigated to remove and/or degrade cyanotoxins with advanced oxidation processes (AOPs) being among the most promising and effective for water detoxification. In this study, the degradation of CYN by sulfate radical-based UV-254 nm-AOPs was evaluated. The UV/S2O8(2-) (UV/peroxydisulfate) was more efficient than UV/HSO5(-) (UV/peroxysulfate) and UV/H2O2 (UV/hydrogen peroxide) processes when natural water samples were used as reaction matrices. The observed UV fluence based pseudo-first-order rate constants followed the expected order of radical quantum yields. The presence of 200 µM natural organic matter (NOM) as carbon slightly inhibited the destruction of CYN; 1.24 mg L(-1)NO3(-) (nitrate) had no significant influence on the removal efficiency and 50 µg L(-1) Fe(2+) [iron (2+)] or Cu(2+) [copper (2+)] improved the performance of UV/S2O8(2-). The addition of tert-butyl alcohol (t-BuOH; hydroxyl radical scavenger) in the reaction yielded byproducts that indicated specific sites in CYN preferentially attacked by sulfate radicals (SRs). The predominant CYN degradation byproduct was P448 consistent with fragmentation of the C5C6 bond of the uracil ring. The subsequent formation of P420 and P392 through a stepwise loss of carbonyl group(s) further supported the fragmentation pathway at C5C6. The byproduct P432 was identified exclusively as mono-hydroxylation of CYN at tricyclic guanidine ring, whereas P414 was detected as dehydrogenation at the tricyclic ring. The elimination of sulfate group and the opening of tricyclic ring were also observed. The possible degradation pathways of CYN by SR-AOP were presented.

Degradation mechanism of cyanobacterial toxin cylindrospermopsin by hydroxyl radicals in homogeneous UV/H2O2 process.

The degradation of cylindrospermopsin (CYN), a widely distributed and highly toxic cyanobacterial toxin (cyanotoxin), remains poorly elucidated. In this study, the mechanism of CYN destruction by UV-254 nm/H2O2 advanced oxidation process (AOP) was investigated by mass spectrometry. Various byproducts identified indicated three common reaction pathways: hydroxyl addition (+16 Da), alcoholic oxidation or dehydrogenation (-2 Da), and elimination of sulfate (-80 Da). The initiation of the degradation was observed at the hydroxymethyl uracil and tricyclic guanidine groups; uracil moiety cleavage/fragmentation and further ring-opening of the alkaloid were also noted at an extended reaction time or higher UV fluence. The degradation rates of CYN decreased and less byproducts (species) were detected using natural water matrices; however, CYN was effectively eliminated under extended UV irradiation. This study demonstrates the efficiency of CYN degradation and provides a better understanding of the mechanism of CYN degradation by hydroxyl radical, a reactive oxygen species that can be generated by most AOPs and is present in natural water environment.

Light activation of Staphylococcus aureus toxin YoeBSa1 reveals guanosine-specific endoribonuclease activity.

The Staphylococcus aureus chromosome harbors two homologues of the YefM-YoeB toxin-antitoxin (TA) system. The toxins YoeBSa1 and YoeBSa2 possess ribosome-dependent ribonuclease (RNase) activity in Escherichia coli. This activity is similar to that of the E. coli toxin YoeBEc, an enzyme that, in addition to ribosome-dependent RNase activity, possesses ribosome-independent RNase activity in vitro. To investigate whether YoeBSa1 is also a ribosome-independent RNase, we expressed YoeBSa1 using a novel strategy and characterized its in vitro RNase activity, sequence specificity, and kinetics. Y88 of YoeBSa1 was critical for in vitro activity and cell culture toxicity. This residue was mutated to o-nitrobenzyl tyrosine (ONBY) via unnatural amino acid mutagenesis. YoeBSa1-Y88ONBY could be expressed in the absence of the antitoxin YefMSa1 in E. coli. Photocaged YoeBSa1-Y88ONBY displayed UV light-dependent RNase activity toward free mRNA in vitro. The in vitro ribosome-independent RNase activity of YoeBSa1-Y88ONBY, YoeBSa1-Y88F, and YoeBSa1-Y88TAG was significantly reduced or abolished. In contrast to YoeBEc, which cleaves RNA at both adenosine and guanosine with a preference for adenosine, YoeBSa1 cleaved mRNA specifically at guanosine. Using this information, a fluorometric assay was developed and used to determine the kinetic parameters for ribosome-independent RNA cleavage by YoeBSa1.

Hydroxyl radical oxidation of cylindrospermopsin (cyanobacterial toxin) and its role in the photochemical transformation.

Cylindrospermopsin (CYN), an alkaloid guanidinium sulfated toxin, is produced by a number of cyanobacteria regularly found in lakes, rivers, and reservoirs. Steady-state and time-resolved radiolysis methods were used to determine reaction pathways and kinetic parameters for the reactions of hydroxyl radical with CYN. The absolute bimolecular reaction rate constant for the reaction of hydroxyl radical with CYN is (5.08 ± 0.16) × 10(9) M(-1) s(-1). Comparison of the overall reaction rate of CYN with hydroxyl radical with the individual reaction rate for addition to the uracil ring in CYN indicate the majority of the hydroxyl radicals (84%) react at the uracil functionality of CYN. Product analyses using liquid chromatography-mass spectrometry indicate the major products from the reaction of hydroxyl radical with CYN involve attack of hydroxyl radical at the uracil ring and hydrogen abstraction from the hydroxy-methine bridge linking the uracil ring to the tricyclic guanidine functionality. The role of hydroxyl radical initiated pathways in the natural organic matter (NOM) photosensitized transformation of CYN were evaluated. Scavenger and trapping experiments indicate that hydroxyl radical mediated transformations account for approximately ~70% of CYN destruction in surface waters under solar irradiation in the presence of NOM. The absence of solvent isotope effect indicates singlet oxygen does not play a significant role in the NOM sensitized transformation of CYN. The primary degradation pathways for HO• mediated and NOM photosensitized destruction of CYN involve destruction of the uracil ring. The fundamental kinetic parameters determined from these studies are critical for the accurate evaluation of hydroxyl-radical based technologies for the remediation of this problematic cyanotoxin in drinking water and important in the assessment of the environmental oxidative transformation of uracil based compounds.

Kinetic and mechanistic study of microcystin-LR degradation by nitrous acid under ultraviolet irradiation.

Degradation of microcystin-LR (MC-LR) in the presence of nitrous acid (HNO(2)) under irradiation of 365nm ultraviolet (UV) was studied for the first time. The influence of initial conditions including pH value, NaNO(2) concentration, MC-LR concentration and UV intensity were studied. MC-LR was degraded in the presence of HNO(2); enhanced degradation of MC-LR was observed with 365nm UV irradiation, caused by the generation of hydroxyl radicals through the photolysis of HNO(2). The degradation processes of MC-LR could well fit the pseudo-first-order kinetics. Mass spectrometry was applied for identification of the byproducts and the analysis of degradation mechanisms. Major degradation pathways were proposed according to the results of LC-MS analysis. The degradation of MC-LR was initiated via three major pathways: attack of hydroxyl radicals on the conjugated carbon double bonds of Adda, attack of hydroxyl radicals on the benzene ring of Adda, and attack of nitrosonium ion on the benzene ring of Adda.

Efficient removal of microcystin-LR by UV-C/H2O2 in synthetic and natural water samples.

The destruction of the commonly found cyanobacterial toxin, microcystin-LR (MC-LR), in surface waters by UV-C/H(2)O(2) advanced oxidation process (AOP) was studied. Experiments were carried out in a bench scale photochemical apparatus with low pressure mercury vapor germicidal lamps emitting at 253.7 nm. The degradation of MC-LR was a function of UV fluence. A 93.9% removal with an initial MC-LR concentration of 1 µM was achieved with a UV fluence of 80 mJ/cm(2) and an initial H(2)O(2) concentration of 882 µM. When increasing the concentration of MC-LR only, the UV fluence-based pseudo-first order reaction rate constant generally decreased, which was probably due to the competition between by-products and MC-LR for hydroxyl radicals. An increase in H(2)O(2) concentration led to higher removal efficiency; however, the effect of HO scavenging by H(2)O(2) became significant for high H(2)O(2) concentrations. The impact of water quality parameters, such as pH, alkalinity and the presence of natural organic matter (NOM), was also studied. Field water samples from Lake Erie, Michigan and St. Johns River, Florida were employed to evaluate the potential application of this process for the degradation of MC-LR. Results showed that the presence of both alkalinity (as 89.6-117.8 mg CaCO(3)/L) and NOM (as ∼2 to ∼9.5 mg/L TOC) contributed to a significant decrease in the destruction rate of MC-LR. However, a final concentration of MC-LR bellow the guideline value of 1 µg/L was still achievable under current experimental conditions when an initial MC-LR concentration of 2.5 µg/L was spiked into those real water samples.

Removal of microorganisms and their chemical metabolites from water using semiconductor photocatalysis.

Semiconductor photocatalysis has been applied to the remediation of an extensive range of chemical pollutants in water over the past 30 years. The application of this versatile technology for removal of micro-organisms and cyanotoxins has recently become an area that has also been the subject of extensive research particularly over the past decade. This paper considers recent research in the application of semiconductor photocatalysis for the treatment of water contaminated with pathogenic micro-organisms and cyanotoxins. The basic processes involved in photocatalysis are described and examples of recent research into the use of photocatalysis for the removal of a range of microorganisms are detailed. The paper concludes with a review of the key research on the application of this process for the removal of chemical metabolites generated from cyanobacteria.

UV protectants for the biopesticide based on Bacillus sphaericus Neide and their role in protecting the binary toxins from UV radiation.

The UV protectant properties of 26 natural and synthetic compounds were investigated for a biopesticide based on an indigenously isolated strain (ISPC-8) of Bacillus sphaericus Neide. In initial screening, spores of ISPC-8 with 0.1% (w/w for solid and v/w for liquid materials) concentration of different compounds were exposed to UV-B radiation (4.9 x 10(5) J/m(2)) for 6h and their spore viability and larvicidal activity were studied. The larvicidal activity was evaluated against third-instar larvae of Culex quinquefasciatus Say. There was a complete loss of spore viability (1.4% viable spores) and partial reduction in larvicidal activity (57.7% of original activity) after exposure of spores to UV-B for 6h. However, spore viability as well as larvicidal activity protected significantly when spores were mixed with different compounds before exposing them to UV-B. Among the different compounds tested benzaldehyde, congo red, para-aminobenzoic acid (PABA) and cinnamaldehyde were found to be promising in protecting the spores from UV-B radiation. The presence of binary toxins (41.9 kDa and 51.4 kDa) in protected and unprotected samples were examined by SDS-PAGE. The binary toxin bands disappeared in unprotected spores after 24h of exposure to UV-B, whereas toxin bands were distinctly visible when spores with benzaldehyde and cinnamaldehyde were exposed to UV-B for 96 h and 120 h, respectively. Congo red and PABA were found to be most effective in protecting binary toxins even after 168 h of exposure to UV-B. Incorporation of these promising UV protectant compounds in biopesticides would help in protecting the spores from the adverse effects of UV radiation and prolong the persistence of biopesticides under field conditions.

Cyanobacterial toxin removal in drinking water treatment processes and recreational waters.

Although federal drinking water regulations determine the quality of potable water, many specifics influence how each utility chooses to treatment water. Some of the specifics include source water quality, storage capacity, existing unit process, and space. An overview of the US recreational and drinking water regulations were discussed in context of cyanobacterial toxin removal and inactivation by ancillary as well as auxiliary treatment practices. Ancillary practice refers to the removal or inactivation of algal toxins by standard daily operational procedures where auxiliary treatment practice refers to intentional treatment. An example of auxiliary treatment would be the addition of powder activated carbon to remove taste and odor compounds. The implementation of new technologies as such ultraviolet disinfection and membrane filtration, to meet current and purposed regulations, can greatly affect the algal toxin removal and inactivation efficiencies. A discussion on meeting the current regulations by altering chemical disinfection, ozone, chlorine, chloramines and chlorine dioxide included their ancillary effects on the protection against algal toxins. Although much of the research has been on the efficiency of the removal and inactivation of microcystin LR and several microcystin variants, the discussion included other algal toxins: anatoxin-a, saxitoxins, and cyclindrospermopsin.

LC/MS/MS structure elucidation of reaction intermediates formed during the TiO(2) photocatalysis of microcystin-LR.

Microcystin-LR (MC-LR), a cyanotoxin and emerging drinking water contaminant, was treated with TiO(2) photocatalysts immobilized on stainless steel plates as an alternative to nanoparticles in slurry. The reaction intermediates of MC-LR were identified with mass spectrometry (MS) at pH of Milli-Q water (pH(sq)=5.7). Eleven new [M+H](+) were observed in the liquid chromatography mass spectrometry (LC/MS) chromatogram with some of them giving multiple peaks. Most of these reaction intermediates have not been reported from previous studies employing TiO(2) nanoparticles at acidic conditions (pH=4.0). Investigating the effects of pH (for 3.0

Mesoporous nitrogen-doped TiO2 for the photocatalytic destruction of the cyanobacterial toxin microcystin-LR under visible light irradiation.

The presence of the harmful cyanobacterial toxins in water resources worldwide drives the development of an innovative and practical water treatment technology with great urgency. This study deals with two important aspects: the fabrication of mesoporous nitrogen-doped TiO2 (N-TiO2) photocatalysts and their environmental application for the destruction of microcystin-LR (MC-LR) under visible light. In a nanotechnological sol-gel synthesis method, a nitrogen-containing surfactant (dodecylammonium chloride) was introduced as a pore templating material for tailor-designing the structural properties of TiO2 and as a nitrogen dopant for its visible light response. The resulting N-TiO2 exhibited significantly enhanced structural properties including 2-8 nm mesoporous structure (porosity 44%) and high surface area of 150 m2/g. Red shift in light absorbance up to 468 nm, 0.9 eV lower binding energy of electrons in Ti 2p state, and reduced interplanar distance of crystal lattices proved nitrogen doping in the TiO2 lattice. Due to its narrow band gap at 2.65 eV, N-TiO2 efficiently degraded MC-LR under visible spectrum above 420 nm. Acidic condition (pH 3.5) was more favorable for the adsorption and photocatalytic degradation of MC-LR on N-TiO2 due to electrostatic attraction forces between negatively charged MC-LR and +6.5 mV charged N-TiO2. Even under UV light, MC-LR was decomposed 3-4 times faster using N-TiO2 than control TiO2. The degradation pathways and reaction intermediates of MC-LR were not directly related to the energy source for TiO2 activation (UV and visible) and nature of TiO2 (neat and nitrogen-doped). This study implies a strong possibility for the in situ photocatalytic remediation of contaminated water with cyanobacterial toxins and other toxic compounds using solar light, a sustainable source of energy.

Protein electrostriction: a possibility of elastic deformation of the alpha-hemolysin channel by the applied field.

While conformational flexibility of proteins is widely recognized as one of their functionally crucial features and enjoys proper attention for this reason, their elastic properties are rarely discussed. In ion channel studies, where the voltage-induced or ligand-induced conformational transitions, gating, are the leading topic of research, the elastic structural deformation by the applied electric field has never been addressed at all. Here we examine elasticity using a model channel of known crystal structure-Staphylococcus aureus alpha-hemolysin. Working with single channels reconstituted into planar lipid bilayers, we first show that their ionic conductance is asymmetric with voltage even at the highest salt concentration used where the static charges in the channel interior are maximally shielded. Second, choosing 18-crown-6 as a molecular probe whose size is close to the size of the narrowest part of the alpha-hemolysin pore, we analyze the blockage of the channel by the crown/K(+) complex. Analysis of the blockage within the framework of the Woodhull model in its generalized form demonstrates that the model is able to correctly describe the crown effect only if the parameters of the model are considered to be voltage-dependent. Specifically, one has to include either a voltage-dependent barrier for crown release to the cis side of the channel or voltage-dependent interactions between the binding site and the crown. We suggest that the voltage sensitivity of both the ionic conductance of the channel seen at the highest salt concentration and its blockage by the crown reflects a field-induced deformation of the pore.

Melanin pigment formation and increased UV resistance in Bacillus thuringiensis following high temperature induction.

The pigment melanin is well known to protect against the damaging effects of UV radiation. In this study, we show that thirty-five of thirty-seven tested Bacillus thuringiensis strains possess the potential to produce melanin in the presence of L-tyrosin at elevated temperature (42 degrees C). These findings offer a method of protecting insecticidal toxins produced by B. thuringiensis from UV degredation and may therefore have important applications in the field of crop protection. Toxicity assays on Heliothis armigera suggested that the insecticidal activity of B. thuringiensis that produced melanin was significantly higher after UV irradiation than when melanin was not produced.

Protection from UV-B damage of mosquito larvicidal toxins from Bacillus thuringiensis subsp. israelensis expressed in Anabaena PCC 7120.

A transgenic strain of the nitrogen-fixing filamentous cyanobacterium Anabaena PCC 7120 protected expressed delta-endotoxin proteins of Bacillus thuringiensis subsp. israelensis from damage inflicted by UV-B, a sunlight component that penetrates Earth's ozone layer. This organism, which serves as a food source to mosquito larvae and could multiply in their breeding sites, may solve the environment-imposed limitations of B. thuringiensis subsp. israelensis as a mosquito biological control agent.

Stability of microcystins from cyanobacteria--IV. Effect of chlorination on decomposition.

Microcystins, the cyclic heptapeptide toxins produced by cyanobacteria such as Microcystis, show tumor-promoting activity through inhibition of protein phosphatases 1 and 2A. They potentially threaten human health, and are increasing the world-wide interest in the health risk associated with cyanobacterial toxins. In this study, the effect of chlorination on the decomposition of microcystins-LR and -RR was examined. The toxins were easily decomposed by chlorination with sodium hypochlorite, and the decomposition depended on the free chlorine dose. In this operation, many reaction products were formed, one of which was determined to be dihydroxymicrocystin formed through the chloronium ion at the conjugated diene of Adda [3-amino-9-methoxy-10-phenyl-2,6,8-trimethyl-deca-4(E), 6(E)-dienoic acid], followed by hydrolysis. Other products may be its stereoisomers and/or regioismers. No noxious products were detected from the chlorination process of microcystin-LR. Although these results suggested that chlorination at an adequate chlorine dose is very effective for the removal of microcystin in raw water, preoxidation of the cell itself with chlorine must be avoided, because it frequently causes toxin release from algae and produce trihalomethanes during water treatment.