Enzymatic properties of a bacterial microcystinase A produced in Saccharomyces cerevisiae.

Microcystins (MCs), which are produced by cyanobacteria, are one of the most serious problems that threaten quality of drinking water and public health. In this study, an electrolysis cell with no electrolyte is demonstrated to degrade MCs (MC-RR, MC-YR and MC-LR) in both high and low concentrations. In addition, degradation of MCs was studied under different current densities. The results revealed that the electrolysis cell could degrade MCs successfully. It was observed that degradation of a single MC was faster than mixed types and statistical analysis revealed that the degradation rate of all the three MCs did not show much difference in mixed degradation. Analysis of hydroxyl radical concentration suggested a possible role of the hydroxyl radical in degradation of MCs. We propose that the electrolysis cell could be a promising treatment for effective removal of MCs in situ, especially in water purification plants where low amounts of salts (electrolytes) are present.

Quorum sensing regulates the efficiency of a microcystin-degrading microbial consortium.

Taxonomic and Genotypical Heterogeneity of Microcystin degrading Bacterioplankton in Western Lake Erie

Alkali tolerance and the mechanism of microcystin (MC) degradation were investigated in the MC‐degrading bacterial species, Sphingopyxis sp. C‐1, to better understand the increased MC degradation under the alkaline conditions that arise during the disappearance of water blooms. MC‐degrading bacteria harbour mlrA, mlrB and mlrC that encode MC‐degrading enzymes. Sphingopyxis sp. C‐1 also possesses these genes, as well as the mlrD gene that has been assumed to encode MC and its degradation transporter. This study demonstrated that MC degradation activity was promoted by the intermittent addition of microcystin‐LR (MCLR) to cultures of strain C‐1. That the expression of mlrA, mlrB and mlrC is induced by MCLR also was indicated, whereas that of mlrA and mlrB is induced by the MCLR degradation products linear MC, H‐Adda‐Glu‐Mdha‐Ala‐OH (tetra peptide) and 2S, 3S, 8S, 9S‐3‐amino‐9‐methoxy‐2, 6, 8‐trimethyl‐10‐phenyldeca‐4E, 6E‐dienoic acid (Adda). Adda played a key role in the induction of mlrA and mlrB gene expression, and the cyclic structure of MCLR was closely associated with the induction of mlrC gene expression. It is suggested, therefore, that Adda is an essential part of a signalling molecule involved in cell‐to‐cell communication. Finally, the MC‐degrading bacteria responded to MCLR and its degradation products by degrading the MlrA, MlrB and MlrC enzymes through a sequential chain reaction for the expression of each.

Cyanobacterial blooms in Thailand waters contain microcystin (MC) hepatotoxins that are a risk to animal and human health. The biodegradation of MCs is a safe and natural method of removal from water. The [Dha7] MC-LR was purified by chromatography, identified by liquid chromatography–tandem mass spectrometry (LC-MS) and used for examining the biodegradation of MCs. Analysis of MC levels revealed degradation of the [Dha7] MC-LR by the bacterium Novosphingobium sp. KKU15, with complete degradation occurring within 3 days under conditions in batches of a flask experiment. The ability of the bacterium to degrade the MCs through a slow sand filter was also investigated. Removal of the [Dha7] MC-LR by biological sand filtration was assessed using a polyvinyl chloride column experiment. In MC-dosed water, degradation of the MC was observed specifically in the inoculated samples (bacterial concentration of 1.6 × 107CFU/cm3 of sand), with complete degradation occurring within 7 days compared to the uninoculated controls. A polymerase chain reaction (PCR) specifically targeting the 16S rRNA gene of Novosphingobium sp. KKU15 was used to monitor the presence of the bacterium in the experimental trials. PCR products indicative of a bacterial population were observed at all of the sample sites in the column where the degradation of the MCs was observed, indicating that this bacterial isolate was active in the degradation of MCs.

Microbial degradation is an important route for removing environmental microcystins (MCs). Here, we investigated the ecological distribution of microcystin degraders (mlr-genotype), and the relationship between the substrate specificity of the microcystin degrader and the profile of microcystin congener production in the habitat. We showed that microcystin degraders were widely distributed and closely associated with Microcystis abundance in Lake Taihu, China. We characterized an indigenous degrader, Sphingopyxis N5 in the northern Lake Taihu, and it metabolized six microcystin congeners in increasing order (RR > LR > YR > LA > LF and LW). Such a substrate-specificity pattern was congruent to the order of the dominance levels of these congeners in northern Lake Taihu. Furthermore, a meta-analysis on global microcystin degraders revealed that the substrate-specificity patterns varied geographically, but generally matched the profiles of microcystin congener production in the degrader habitats, and the indigenous degrader typically metabolized well the dominant MC congeners, but not the rare congeners in the habitat. This highlighted the phenotypic congruence between microcystin production and degradation in natural environments. We theorize that such congruence resulted from the metabolic adaptation of the indigenous degrader to the local microcystin congeners. Under the nutrient microcystin selection, the degraders might have evolved to better exploit the locally dominant congeners. This study provided the novel insight into the ecological distribution and adaptive degradation of microcystin degraders.

Heterotrophic bacteria are suggested as the major agents that degrade microcystins (MCs), a major cyanotoxins, in natural environments. However, little is known of the taxonomic and functional diversity of MC-degrading bacteria in Lake Erie of the Laurentian Great Lakes, the largest freshwater system on earth. This study obtained six bacterial pure isolates from Lake Erie with anability to use MCs as the sole carbon and energy sources. MC degradation rates of the isolates were impacted by temperature and pH. The key gene for MC degradation (mlrA) were failed to be PCR amplified from for all 6 MC degraders, indicating they may possess a novel MC degradation pathway. In addition for potentials used in MC bioremediation, two isolates maybe can offer extra benefits as biofertilizers.

Simultaneous electrochemical removal of three microcystin congeners and sulfamethoxazole in natural water

Microcystins (MCs) are toxic compounds produced by cyanobacteria in eutrophicate water environment and threaten the drinking water quality which often leads to serious sicknesses. MCs are difficult to be removed in water treatment when the concentration is very low but still harmful. When the MC concentration is low (μg/L), filter or some conventional chemical does not work, but UV can keep removing it to a lower level by some active groups. Herein, 185-nm UV irradiation in an immersing mode was used to remove MCs. Compared with the normal radiation mode, the immersing mode showed a remarkable degradation rate of MCs and a greater removal efficiency than the direct radiation. Radicals of ·H and ·OH were produced and strengthened the removal rate, after H2O absorbed 185 nm photons. Three important factors of pH value, initial concentration, and aeration capacity were investigated. When pH was less than 7, a better removal rate by ·H was found, due to the main path of MC degradation and Adda strain removal. When the initial concentration increased, the MC removal ratio decreased because HO· formed near the lamp surface and degraded MC molecules fast. When the aeration capacity improved, the MC removal ratio for the presence of air enforced reaction of dissolved oxygen with hydrated electrons and hydrogen atoms produced in the radiolysis.

The UV-ozone (UV-O3) process is not widely applied in wastewater and potable water treatment partly for the relatively high cost since complicated UV radiation and ozone generating systems are utilized. The UV-microozone (UV-microO3), a new advanced process that can solve the abovementioned problems, was introduced in this study. The effects of air flux, air pressure, and air humidity on generation and concentration of O3in UV-microO3reactor were investigated. The utilization of this UV-microO3reactor in microcystins (MCs) degradation was also carried out. Experimental results indicated that the optimum air flux in the reactor equipped with 37 mm diameter quartz tube was determined to be 18∼25 L/h for efficient O3generation. The air pressure and humidity in UV-microO3reactor should be low enough in order to get optimum O3output. Moreover, microcystin-RR, YR, and LR (MC-RR, MC-YR, and MC-LR) could be degraded effectively by UV-microO3process. The degradation of different MCs was characterized by first-order reaction kinetics. The pseudofirst-order kinetic constants for MC-RR, MC-YR, and MC-LR degradation were 0.0093, 0.0215, and 0.0286 min−1, respectively. Glucose had no influence on MC degradation through UV-microO3. The UV-microO3process is hence recommended as a suitable advanced treatment method for dissolved MCs degradation.

 Abstract—A bacterium, Novosphingobium sp. KKU03 previously demonstrated to degrade the cyanobacterial toxin, microcystins (MCs), was investigated for the removal of MCs through the slow sand filter. In this study, biological sand filtration was assessed in PVC column experiment for its ability to remove MCs ([Dha 7 ]MC-LR and MC-LR). Degradation of MCs was observed with inoculated (6x10 8 CFU/ml) treatment of water dosed with both MCs (completed degradation within 7 days) compared to uninoculated control. Polymerase chain reaction (PCR) specifically targeting amplification of 16S rRNA gene of Novosphingobium sp. KKU03 was applied to monitor the presence of the bacterium in experimental trials. PCR products indicative of an endemic bacterial population were observed at all sample sites through the column where MCs degradation was measured, indicating this bacterial isolate was active in degradation of MCs.

Global concerns over harmful cyanobacterial blooms brought on by eutrophication are now widespread. Aquatic ecological restoration techniques that use algicidal bacteria to control toxic algae show promise. A Bacillus subtilis S4 (S4) strain with strong Microcystis aeruginosa algicidal activity and the capacity to degrade microcystins (MCs) were successfully isolated and evaluated in this study. The dynamics of internal and extracellular MC concentration as well as the physiological response and morphological properties of M. aeruginosa were investigated in the M. aeruginosa/bacteria co-culture system. The findings demonstrated that when S4 density grew from 1 × 106 cells/ml to 1 × 108 cells/ml, the release of M. aeruginosa lysis and MCs was boosted; however, MCs dropped by approximately 90% within 18 h, regardless of bacterial density. Comparing the bacterial cell incubation system to the control and bacterial cell-free filtrate systems, the assessment of extracellular and intracellular MCs revealed a 95% reduction in MCs. The findings showed that 89% of MCs were decreased by bacterial cells, while 98% of M. aeruginosa cells were algaecided by bacterial metabolites. Sustainable eradication of M. aeruginosa and MCs has been accomplished by the combined efforts of the S4 strain and its metabolites. By secreting algicidal chemicals that are resistant to proteases, acid, base, and heat, the S4 strain indirectly acts as an algaecide. The S4 strain possesses a strong ability to break down MCs and a very effective and stable algaecide function, indicating that it can potentially treat eutrophic water with hazardous algae.

Biodegradation mechanism of microcystin-LR by a novel isolate of Rhizobium sp. TH and the evolutionary origin of the mlrA gene

Microcystins (MCs) are the most toxic and abundant cyanotoxins found in natural waters during harmful cyanobacterial blooms. These toxins pose a significant threat to plant, animal, and human health due to their toxicity. Degradation of MCs by MC-degrading bacteria is a promising method for controlling these toxins, demonstrating safety, high efficiency, and cost-effectiveness. In this study, we isolated potential MC-degrading bacteria (strains TA13, TA14, and TA19) from Lake Kasumigaura in Japan and found that they possess a high capacity for MC degradation. Based on 16S rRNA gene sequencing, all three isolated strains were identified as belonging to the Klebsiella species. These bacteria effectively degraded MC-RR, MC-YR, and MC-LR under various temperature and pH conditions within 10 h, with the highest degrading activity and degradation rate observed at 40 °C. Furthermore, the isolated strains efficiently degraded MCs not only under neutral pH conditions, but also in alkaline environments. Additionally, we detected the MC-degrading gene (mlrA) in all three isolated strains, marking the first report of the mlrA gene in Klebsiella species. The copy number of the mlrA gene in the strains increased after exposure to MCs. These findings indicate that strains TA13, TA14, and TA19 significantly contribute of MC bioremediation in Lake Kasumigaura during cyanobacterial blooms.

Harmful cyanobacterial blooms (HCBs) frequently occur in eutrophic freshwater ecosystems worldwide. Microcystins (MCs) are considered to be the most prominent and toxic metabolites during HCBs. MCs may be harmful to human and animal health through drinking water and recreational water. Biodegradation is eco-friendly, cost-effective and one of the most effective methods to remove MCs. Many novel MC-degrading bacteria and their potential for MCs degradation have been documented. However, it is a challenge to apply the free MC-degrading bacterial cells in natural environments due to the long-term operational instability and difficult recycling. Immobilization is the process of restricting the mobility of bacteria using carriers, which has several advantages as biocatalysts compared to free bacterial cells. Biological water treatment systems with microbial immobilization technology can potentially be utilized to treat MC-polluted wastewater. In this review article, various types of supporting materials and methods for microbial immobilization and the application of bacterial immobilization technology for the treatment of MCs-contaminated water are discussed. This article may further broaden the application of microbial immobilization technology to the bioremediation of MC-polluted environments.