Characteristics of a microcystin-LR biodegrading bacterial isolate: Ochrobactrum sp. FDT5

Review: Current understanding on biological filtration for the removal of microcystins

Harmful algal blooms (HABs) have become a global problem not only in aquatic habitats but also in public health and safety due to the production of cyanotoxins as their secondary metabolites. Among the various identified cyanotoxin groups, microcystins (MCs) are one of the most prevalent cyanotoxin detected during HABs. Different strategies including advanced physical and chemical treatment processes have been developed to mitigate the threat of cyanotoxins in water utilities, but these have revealed certain limitations in terms of high operational costs, low removal efficacy, and harmful by-products formation. Recently, biological filtration systems (BFS) have gained attention for safe drinking water production as they can treat various natural organic matter (NOM) and emerging contaminants through a highly efficient and environmentally sustainable process. However, limited attention has been given to understand the current research progress, research challenges, and knowledge gaps for the successful implementation of BFS for MC removal. Therefore, in this review, currently identified MC biodegradation pathways and MC-degrading microorganisms with their degradation rates are summarized, which may be pivotal for studying bioaugmented BFS to enhance the MC removal during HABs. Moreover, both laboratory and field studies on BFS for MC removal are reviewed, followed by a discussion of current challenges and future research needs for the practical application of BFS.

Immobilization of Microbes for Biodegradation of Microcystins: A Mini Review

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.

Optimization of Biodegradation Characteristics of Sphingopyxis sp. YF1 against Crude Microcystin-LR Using Response Surface Methodology

Sphingopyxis sp. YF1 has proven to be efficient in biodegrading microcystin (MC)-leucine (L) and arginine (R) (MC-LR); however, the optimal environmental factors to biodegrade the toxin have not been investigated. In this study, the biodegrading characteristics of strain YF1 against MC-LR were assessed under diverse environmental factors, including temperature (20, 30 or 40 °C), pH (5, 7 or 9) and MC-LR concentration (1, 3 or 5 µg/mL). Data obtained from the single-factor experiment indicated that MC-LR biodegradation by strain YF1 was temperature-, pH- and MC-LR-concentration-dependent, and the maximal biodegradation rate occurred at 5 µg/mL/h. Proposing Box-Behnken Design in response surface methodology, the influence of the three environmental factors on the biodegradation efficiency of MC-LR using strain YF1 was determined. A 17-run experiment was generated and carried out, including five replications performed at the center point. The ANOVA analysis demonstrated that the model was significant, and the model prediction of MC-LR biodegradation was also validated with the experimental data. The quadratic statistical model was established to predict the interactive effects of the environmental factors on MC-LR biodegradation efficiency and to optimize the controlling parameters. The optimal conditions for MC-LR biodegradation were observed at 30 °C, pH 7 and 3 µg/mL MC-LR, with a biodegradation efficiency of 100% after 60 min. The determination of the optimal environmental factors will help to unveil the detailed biodegradation mechanism of MC-LR by strain YF1 and to apply it into the practice of eliminating MC-LR from the environment.

Antimicrobial activity against Microcystis aeruginosa and degradation of microcystin-LR by bacteria isolated from Antarctica

Cyanobacteria massive proliferations are common in freshwater bodies worldwide, causing adverse effects on aquatic ecosystems and public health. Numerous species develop blooms. Most of them correspond to the toxic microcystin-producing cyanobacterium Microcystis aeruginosa. Microorganisms recovered from Antarctic environment can be considered an unexploited source of antimicrobial compounds. Data about their activity against cyanobacteria are scant or inexistent. This study aimed to evaluate the capacity of Antarctic bacteria to inhibit the proliferation of M. aeruginosa BCPUSP232 and to degrade microcystin-LR (MC-LR). Cell-free extracts of seventy-six bacterial strains were initially tested for antimicrobial activity. Unidentified (UN) strains 62 and ES7 and Psychromonas arctica were able to effectively lyse M. aeruginosa. Eight strains showed MIC ranging from 0.55 to 3.00 mg mL^-1, with ES7 showing the best antimicrobial activity. Arthrobacter sp. 443 and UN 383 were the most efficient in degrading MC-LR, with 24.87 and 23.85% degradation, respectively. To our knowledge, this is the first report of antimicrobial and MC-LR degradation activities by Antarctic bacteria, opening up perspectives for their future application as an alternative or supporting approach to help mitigate cyanobacterial blooms.

A Mini Review on Microcystins and Bacterial Degradation

Microcystins (MCs) classified as hepatotoxic and carcinogenic are the most commonly reported cyanobacterial toxins found in the environment. Microcystis sp. possessing a series of MC synthesis genes (mcyA-mcyJ) are well documented for their excessive abundance, numerous bloom occurrences and MC producing capacity. About 246 variants of MC which exert severe animal and human health hazards through the inhibition of protein phosphatases (PP1 and PP2A) have been characterized. To minimize and prevent MC health consequences, the World Health Organization proposed 1 µg/L MC guidelines for safe drinking water quality. Further the utilization of bacteria that represent a promising biological treatment approach to degrade and remove MC from water bodies without harming the environment has gained global attention. Thus the present review described toxic effects and bacterial degradation of MCs.

Importance of bacterial biodegradation and detoxification processes of microcystins for environmental health

Microcystins (MC) the most frequently reported cyanobacterial harmful algal bloom toxins primarily found in some species of freshwater genera pose a serious threat to human and animal health. To reduce health risks associated with MC exposure it is important to remove these toxins found in drinking and recreational waterbodies. Since the physical and chemical water treatment methods are inefficient in completely degrading MC, alternative approaches to effectively detoxify MC have become the focus of global research. The aim of this review was to provide the current approach to cost-effective biological treatment methods which utilize bacteria to degrade MC without generation of harmful by-products. In addition, the catabolic pathways involved in MC-degradation involving proteins encoded mlr gene cluster, intermediate products and efficiencies of bacteria strain/bacteria community are presented and compared.

The biodegradation of microcystins in temperate freshwater bodies with previous cyanobacterial history

Cyanobacterial blooms and cyanotoxins occur in freshwater lakes and reservoirs all over the world. Bacterial degradation of microcystins (MC), hepatotoxins produced by several cyanobacterial species, has also been broadly documented. However, information regarding MC biodegradation in European water bodies is very limited. In this paper, the occurrence and identification of MC biodegradation products was documented for 21 European lakes and reservoirs, many of which have well-documented cyanobacterial bloom histories. Varying cyanobacterial abundance and taxonomical composition were documented and MC producers were found in all the analysed samples. Planktothrix agardhii was the most common cyanobacterial species and it formed mass occurrences in four lakes. MC biodegradation was observed in 86% of the samples (18 out of 21), and four products of dmMC-LR decomposition were detected by HPLC and LC-MS methods. The two main products were cyclic dmMC-LR with modifications in the Arg-Asp-Leu region; additionally one product was recognized as the tetrapeptide Adda-Glu-Mdha-Ala. The composition of the detected products suggested a new biochemical pathway of MC degradation. The results confirmed the hypothesis that microcystin biodegradation is a common phenomenon in central European waters and that it may occur by a mechanism which is different from the one previously reported. Such a finding implies the necessity to develop a more accurate methodology for screening bacteria with MC biodegradation ability. Furthermore, it warrants new basic and applied studies on the characterization and utilization of new MC-degrading strains and biodegradation pathways.

Current research scenario for microcystins biodegradation - A review on fundamental knowledge, application prospects and challenges

Microcystins (MCs) are common cyanotoxins produced by harmful cyanobacterial blooms (HCBs) and severely threaten human and ecosystems health. Biodegradation is an efficient and sustainable biological strategy for MCs removal. Many novel findings in fundamental knowledge and application potential of MC-biodegradation have been documented. Little effort has devoted to summarize and comment recent research progress on MC-biodegradation, and discuss the research problems and gaps. This review deals with current research scenario in aerobic and anaerobic biodegradation for MCs. Diverse organisms capable of degrading MCs are encapsulated. Enzymatic mechanisms and influence factors regulating aerobic and anaerobic MC-biodegradation are summarized and discussed, which are essential for assessing and reducing MC-risks during HCBs episodes. Also, we propose some ideas to solve the challenges and bottleneck problems in practical application of MC-biodegradation, and discuss research gaps and promising research methods which deserve special attention. This review may provide new insights on future direction of MC-biodegradation research, in order to further broaden its application prospects for bioremediation.

Microcystin-degrading bacteria affect mcyD expression and microcystin synthesis in Microcystis spp

Cyanobacterial blooms occur increasingly often and cause ecological, economic and human health problems worldwide. Microcystins (MCs) are the dominant toxins produced by cyanobacteria and are implicated in epidemic disease and environmental problems. Extensive research has been reported on the various regulating factors, e.g., light, temperature, nutrients such as nitrogen and phosphorus, pH, iron, xenobiotics, and predators, that influence microcystin (MC) synthesis, but little is known about the effects of cyanobacteria-associated bacteria on MC synthesis. A considerable number of studies have focused on interactions between Microcystis species and their associated bacteria. In this study, we evaluated the effects of MC-degrading bacteria (MCDB) on MC synthesis gene mcyD expression and MC synthesis in axenic strain PCC7806, non-axenic strain FACHB905, and colony strain FACHB1325 of Microcystis by quantitative real-time polymerase chain reaction (RT-PCR) assay and enzyme-linked immunosorbent assay (ELISA). We demonstrate for the first time that MCDB can induce and up-regulate the MC production and transcriptional response of the mcyD gene of toxic Microcystis. On day 4 of the culturing experiment, the intracellular MC concentration and transcriptional response of mcyD of FACHB1325 were up-regulated 1.9 and 5.3-fold over that of the control, and for FACHB905 were up-regulated 1.8 and 4.2-fold over that of the control, respectively. On day 10, the transcriptional response of mcyD was up-regulated 21.3-fold in PCC7806. These results indicate that there are interactions between toxic Microcystis and MCDB, and MCDB may play a role in regulating mcyD expression in toxic Microcystis.

Bloom Dynamics of Cyanobacteria and Their Toxins: Environmental Health Impacts and Mitigation Strategies

Cyanobacteria are ecologically one of the most prolific groups of phototrophic prokaryotes in both marine and freshwater habitats. Both the beneficial and detrimental aspects of cyanobacteria are of considerable significance. They are important primary producers as well as an immense source of several secondary products, including an array of toxic compounds known as cyanotoxins. Abundant growth of cyanobacteria in freshwater, estuarine, and coastal ecosystems due to increased anthropogenic eutrophication and global climate change has created serious concern toward harmful bloom formation and surface water contamination all over the world. Cyanobacterial blooms and the accumulation of several cyanotoxins in water bodies pose severe ecological consequences with high risk to aquatic organisms and global public health. The proper management for mitigating the worldwide incidence of toxic cyanobacterial blooms is crucial for maintenance and sustainable development of functional ecosystems. Here, we emphasize the emerging information on the cyanobacterial bloom dynamics, toxicology of major groups of cyanotoxins, as well as a perspective and integrative approach to their management.

UV-B Exposure Affects the Biosynthesis of Microcystin in Toxic Microcystis aeruginosa Cells and Its Degradation in the Extracellular Space

Microcystins (MCs) are cyclic hepatotoxic heptapeptides produced by cyanobacteria that can be toxic to aquatic and terrestrial organisms. MC synthesis and degradation are thought to be influenced by several different physical and environmental parameters. In this study, the effects of different intensities of UV-B radiation on MC biosynthesis in Microcystis cells and on its extracellular degradation were investigated by mRNA analysis and degradation experiments. Exposure to UV-B at intensities of 1.02 and 1.45 W/m² not only remarkably inhibited the growth of Microcystis, but also led to a decrease in the MC concentration. In addition, mcyD transcription was decreased under the same UV-B intensities. These results demonstrated that the effects of UV-B exposure on the biosynthesis of MCs in Microcystis cells could be attributed to the regulation of mcy gene transcription. Moreover, the MC concentration was decreased significantly after exposure to different intensities of UV-B radiation. Of the three MC variants (MC-LR, -RR and -YR, L, R and Y are abbreviations of leucine, arginine and tyrosine), MC-LR and MC-YR were sensitive to UV-B radiation, whereas MC-RR was not. In summary, our results showed that UV-B radiation had a negative effect on MC production in Microcystis cells and MC persistence in the extracellular space.