Immobilization of Microbes for Biodegradation of Microcystins: A Mini Review

Comparative genomic analysis and functional investigations for MCs catabolism mechanisms and evolutionary dynamics of MCs-degrading bacteria in ecology

Microcystins (MCs) significantly threaten the ecosystem and public health. Biodegradation has emerged as a promising technology for removing MCs. Many MCs-degrading bacteria have been identified, including an indigenous bacterium Sphingopyxis sp. YF1 that could degrade MC-LR and Adda completely. Herein, we gained insight into the MCs biodegradation mechanisms and evolutionary dynamics of MCs-degrading bacteria, and revealed the toxic risks of the MCs degradation products. The biochemical characteristics and genetic repertoires of strain YF1 were explored. A comparative genomic analysis was performed on strain YF1 and six other MCs-degrading bacteria to investigate their functions. The degradation products were investigated, and the toxicity of the intermediates was analyzed through rigorous theoretical calculation. Strain YF1 might be a novel species that exhibited versatile substrate utilization capabilities. Many common genes and metabolic pathways were identified, shedding light on shared functions and catabolism in the MCs-degrading bacteria. The crucial genes involved in MCs catabolism mechanisms, including mlr and paa gene clusters, were identified successfully. These functional genes might experience horizontal gene transfer events, suggesting the evolutionary dynamics of these MCs-degrading bacteria in ecology. Moreover, the degradation products for MCs and Adda were summarized, and we found most of the intermediates exhibited lower toxicity to different organisms than the parent compound. These findings systematically revealed the MCs catabolism mechanisms and evolutionary dynamics of MCs-degrading bacteria. Consequently, this research contributed to the advancement of green biodegradation technology in aquatic ecology, which might protect human health from MCs.

Evaluating microcystinase A-based approach on microcystins degradation during harvested cyanobacterial blooms

Addressing notorious and worldwide Microcystis blooms, mechanical algae harvesting is an effective emergency technology for bloom mitigation and removal of nutrient loads in waterbodies. However, the absence of effective methods for removal of cyanobacterial toxins, e.g., microcystins (MCs), poses a challenge to recycle the harvested Microcystis biomass. In this study, we therefore introduced a novel approach, the "captured biomass-MlrA enzymatic MC degradation", by enriching microcystinase A (MlrA) via fermentation and spraying it onto salvaged Microcystis slurry to degrade all MCs. After storing the harvested Microcystis slurry, a rapid release of extracellular MCs occurred within the initial 8 h, reaching a peak concentration of 5.33 μg/mL at 48 h during the composting process. Upon spraying the recombinant MlrA crude extract (about 3.36 U) onto the Microcystis slurry in a ratio of 0.1% (v/v), over 95% of total MCs were degraded within a 24-h period. Importantly, we evaluated the reliability and safety of using MlrA extracts to degrade MCs. Results showed that organic matter/nutrient contents, e.g. soluble proteins, polysaccharides, phycocyanin and carotenoids, were not significantly altered. Furthermore, the addition of MlrA extracts did not significantly change the bacterial community composition and diversity in the Microcystis slurry, indicating that the MlrA extracts did not increase the risk of pathogenic bacteria. Our study provides an effective and promising method for the pre-treatment of harvested Microcystis biomass, highlighting an ecologically sustainable framework for addressing Microcystis blooms.

Effective microorganism water treatment method for rapid eutrophic reservoir restoration

Since reservoirs perform many important functions, they are exposed to various types of unfavorable phenomena, e.g., eutrophication which leads to a rapid growth of algae (blooms) that degrade water quality. One of the solutions to combat phytoplankton blooms are effective microorganisms (EM). The study aims to evaluate the potential of EM in improving the water quality of the Turawa reservoir on the Mała Panew River in Poland. It is one of the first studies providing insights into the effectiveness of using EM in the bioremediation of water in a eutrophic reservoir. Samples for the study were collected in 2019-2021. The analysis showed that EM could be one of the most effective methods for cleaning water from unfavorable microorganisms (HBN22, HBN36, CBN, FCBN, FEN) - after the application of EM, a reduction in their concentration was observed (from 46.44 to 58.38% on average). The duration of their effect ranged from 17.6 to 34.1 days. The application of EM improved the trophic status of the Turawa reservoir, expressed by the Carlson index, by 7.78%. As shown in the literature review, the use of other methods of water purification (e.g., constructed wetlands, floating beds, or intermittent aeration) leads to an increase in the effectiveness and a prolongation of the duration of the EM action. The findings of the study might serve as a guide for the restoration of eutrophic reservoirs by supporting sustainable management of water resources. Nevertheless, further research should be conducted on the effectiveness of EM and their application in the remediation of eutrophic water reservoirs.

Biosensing of arsenic by whole-cell bacterial bioreporter immobilized on polycaprolactone (PCL) electrospun fiber

In recent years, heavy metals derived from several anthropogenic sources have both direct and indirect detrimental effects on the health of the environment and living organisms. Whole-cell bioreporters (WCBs) that can be used to monitor the levels of heavy metals in drinking and natural spring waters are important. In this study, whole-cell arsenic bacterial bioreporters were immobilized using polycaprolactone (PCL) electrospun fibers as the support material. The aim is to determine the properties of this immobilized bioreporter system by evaluating its performance in arsenic detection. Within the scope of the study, different growth media and fiber immobilization times were tested to determine the parameters affecting the fluorescent signals emitted by the immobilized bioreporter system in the presence of two dominant forms of arsenic, namely arsenite (As(III)) and arsenate (As(V)). In addition, the sensitivity, selectivity, response time, and shelf-life of the developed bioreporter system were evaluated. As far as the literature is concerned, this is the first study to investigate the potential of using PCL-electrospun fiber-immobilized fluorescent bacterial bioreporter for arsenic detection. This study will open new avenues in environmental arsenic monitoring.

The potential of white-rot fungi for algal control: Mechanisms, Strategies, and Challenges

As human society and industrialization have progressed, harmful algal blooms have contributed to global ecological pollution which makes the development of a novel and effective algal control strategy imminent. This is because existing physical and chemical methods for dealing with the problem have issues like cost and secondary pollution. Benefiting from their environmentally friendly and biocompatible properties, white-rot fungi (WRF) have been studied to control algal growth. WRF control algae by using algae for carbon or nitrogen, antagonism, and enhancing allelopathies. It can be better applied to practice by immobilization. This paper reviews the mechanism for WRF control of algae growth and its practical application. It demonstrates the limitations of WRF controlling algae growth and aids the further study of biological methods to regulate eutrophic water in algae growth research. In addition, it provides theoretical support for the fungi controlling algae growth.

Bacteria-Polymer Composite Material for Glycerol Valorization

Bacterial immobilization is regarded as an enabling technology to improve the stability and reusability of biocatalysts. Natural polymers are often used as immobilization matrices but present certain drawbacks, such as biocatalyst leakage and loss of physical integrity upon utilization in bioprocesses. Herein, we prepared a hybrid polymeric matrix that included silica nanoparticles for the unprecedented immobilization of the industrially relevant Gluconobacter frateurii (Gfr). This biocatalyst can valorize glycerol, an abundant by-product of the biodiesel industry, into glyceric acid (GA) and dihydroxyacetone (DHA). Different concentrations of siliceous nanosized materials, such as biomimetic Si nanoparticles (SiNps) and montmorillonite (MT), were added to alginate. These hybrid materials were significantly more resistant by texture analysis and presented a more compact structure as seen by scanning electron microscopy. The preparation including 4% alginate with 4% SiNps proved to be the most resistant material, with a homogeneous distribution of the biocatalyst in the beads as seen by confocal microscopy using a fluorescent mutant of Gfr. It produced the highest amounts of GA and DHA and could be reused for up to eight consecutive 24 h reactions with no loss of physical integrity and negligible bacterial leakage. Overall, our results indicate a new approach to generating biocatalysts using hybrid biopolymer supports.

New perspectives into Gluconobacter-catalysed biotransformations

Different from other aerobic microorganisms that oxidise carbon sources to water and carbon dioxide, Gluconobacter catalyses the incomplete oxidation of various substrates with regio- and stereoselectivity. This ability, as well as its capacity to release the resulting products into the reaction media, place Gluconobacter as a privileged member of a non-model microorganism class that may boost industrial biotechnology. Knowledge of new technologies applied to Gluconobacter has been piling up in recent years. Advancements in its genetic modification, application of immobilisation tools and careful designs of the transformations, have improved productivities and stabilities of Gluconobacter strains or enabled new bioconversions for the production of valuable marketable chemicals. In this work, the latest advancements applied to Gluconobacter-catalysed biotransformations are summarised with a special focus on recent available tools to improve them. From genetic and metabolic engineering to bioreactor design, the most recent works on the topic are analysed in depth to provide a comprehensive resource not only for scientists and technologists working on/with Gluconobacter, but for the general biotechnologist.

Production of Pigments under Submerged Culture through Repeated Batch Fermentation of Immobilized Talaromyces atroroseus GH2

Pigments of natural origin have become a research trend, and fungi provide a readily available alternative source. Moreover, developing novel processes that increase yields, reduce process time and simplify downstream processing is of increased interest. In this sense, this work proposes an alternative for Talaromyces atroroseus GH2 biomass re-utilization to produce pigments through consecutive batches using immobilized mycelium. Different support materials were evaluated for pigment production and immobilization capacity. Then, Taguchi’s method was applied to determine the effect of four factors related to fungal immobilization and pigment production (inoculum concentration, support density, working volume and support volume). Afterward, process kinetics for pigment production using immobilized cells of T. atroroseus GH2 in consecutive batches were evaluated. All evaluated factors were significant and affected pigment production and microorganism growth differently. At improved conditions, immobilization capacity reached 99.01 ± 0.37% and the pigment production was 30% higher than using free cells. Process kinetics showed that the production could continue for three batches and was limited by excessive microorganism growth. Indeed, more studies are still needed, but the immobilization of Talaromyces atroroseus GH2 represents a promising strategy for allowing downstream-processing intensification since immobilized biomass is easily removed from the fermentation media, thus paving the way for the further development of a continuous process.

Combination Effect of Microcystins and Arsenic Exposures on CKD: A Case-Control Study in China

Evidence has shown that exposure to environmental pollutants such as microcystins (MCs), arsenic (As), and cadmium (Cd) can lead to the occurrence and development of chronic kidney disease (CKD). There is a synergistic effect between MCs and Cd. However, the combined effect of MCs and As exposures on CKD remains unclear. In Hunan province, China, 135 controls and 135 CKD cases were enrolled in a case-control study. Serum MCs, plasma As and Cd concentrations were measured for all participants. We investigated the association between MCs/As and CKD risk using conditional logistic regression. The additive model explored the interaction effect, and the Bayesian kernel machine regression (BKMR) models investigated the combined effects of MCs, As, and Cd on CKD. The results showed that MCs and As were significantly associated with CKD risk. Participants in the highest MCs concentration had a 4,81-fold increased risk of CKD compared to those in the lowest quartile (95% confidence interval [CI]: 1,96 to 11,81). The highest quartile of As concentrations corresponded to an adjusted odds ratio of 3.40 (95% CI: 1.51, 7.65) relative to the lowest quartile. MCs/As and CKD risk exhibited significant dose-response correlations (all p for trend < 0.01). In addition, a positive interaction effect of MCs and As on CKD was also reported. The CKD risk due to interaction was 2.34 times (95% CI: 0.14, 4.54) relative to the CKD risk without interaction, and the attributable proportion of CKD due to interaction among individuals with both exposures was 56% (95% CI: 0.22, 0.91). In the BKMR, the combined effect of MCs, As, and Cd was positively associated with CKD. In conclusion, both MCs and As are independent risk factors for CKD, exerting a synergistic effect between them. Combined exposure to MCs, As, and Cd can increase the risk of CKD.

Cyanophage technology in removal of cyanobacteria mediated harmful algal blooms: A novel and eco-friendly method

Cyanophages are highly abundant specific viruses that infect cyanobacterial cells. In recent years, the cyanophages and cyanobacteria interactions drew attention to environmental restoration due to their discovery in marine and freshwater systems. Cyanobacterial harmful algal blooms (cyanoHABs) are increasing throughout the world and contaminating aquatic ecosystems. The blooms cause severe environmental problems including unpleasant odors and cyanotoxin production. Cyanotoxins have been reported to be lethal agents for living beings and can harm animals, people, aquatic species, recreational activities, and drinking water reservoirs. Biological remediation of cyanoHABs in aquatic systems is a sustainable and eco-friendly approach to increasing surface water quality. Therefore, this study compiles the fragmented information with the solution of removal of cyanoHABs using cyanophage therapy techniques. To date, scant information exists in terms of bloom formation, cyanophage occurrence, and mode of action to remediate cyanoHABs. Overall, this study illustrates cyanobacterial toxin production and its impacts on the environment, the mechanisms involved in the cyanophage-cyanobacteria interaction, and the application of cyanophages for the removal of toxic cyanobacterial blooms.

Biodegradation of MC-LR and its key bioactive moiety Adda by Sphingopyxis sp. YF1: Comprehensive elucidation of the mechanisms and pathways

Microcystins (MCs) are harmful to the ecology and public health. Some bacteria can degrade MCs into Adda, but few can destroy Adda. Adda is the key bioactive moiety of MCs and mainly contributes to hepatotoxicity. We had previously isolated an indigenous novel bacterial strain named Sphingopyxis sp. YF1 that can efficiently degrade MCs and its key bioactive moiety Adda, but the mechanisms remained unknown. Here, the biodegradation mechanisms and pathways of Adda were systematically investigated using multi-omics analysis, mass spectrometry and heterologous expression. The transcriptomic and metabolomic profiles of strain YF1 during Adda degradation were revealed for the first time. Multi-omics analyses suggested that the fatty acid degradation pathway was enriched. Specifically, the expression of genes encoding aminotransferase, beta oxidation (β-oxidation) enzymes and phenylacetic acid (PAA) degradation enzymes were significantly up-regulated during Adda degradation. These enzymes were further proven to play important roles in the biodegradation of Adda. Simultaneously, some novel potential degradation products of Adda were identified successfully, including 7‑methoxy-4,6-dimethyl-8-phenyloca-2,4-dienoic acid (C₁₇H₂₂O₃), 2-methyl-3‑methoxy-4-phenylbutyric acid (C₁₂H₁₆O₃) and phenylacetic acid (PAA, C₈H₈O₂). In summary, the Adda was converted into PAA through aminotransferase and β-oxidation enzymes, then the PAA was further degraded by PAA degradation enzymes, and finally to CO₂ via the tricarboxylic acid cycle. This study comprehensively elucidated the novel MC-LR biodegradation mechanisms, especially the new enzymatic pathway of Adda degradation. These findings provide a new perspective on the applications of microbes in the MCs polluted environment.

MC-LR Aggravates Liver Lipid Metabolism Disorders in Obese Mice Fed a High-Fat Diet via PI3K/AKT/mTOR/SREBP1 Signaling Pathway

Obesity, a metabolic disease caused by excessive fat accumulation in the body, has attracted worldwide attention. Microcystin-LR (MC-LR) is a hepatotoxic cyanotoxin which has been reportedly to cause lipid metabolism disorder. In this study, C57BL/6J mice were fed a high-fat diet (HFD) for eight weeks to build obese an animal model, and subsequently, the obese mice were fed MC-LR for another eight weeks, and we aimed to determine how MC-LR exposure affects the liver lipid metabolism in high-fat-diet-induced obese mice. The results show that MC-LR increased the obese mice serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT), indicating damaged liver function. The lipid parameters include serum triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-c), and liver TG, which were all increased, whilst the high-density lipoprotein cholesterol (HDL-c) was decreased. Furthermore, after MC-LR treatment, histopathological observation revealed that the number of red lipid droplets increased, and that steatosis was more severe in the obese mice. In addition, the lipid synthesis-related genes were increased and the fatty acid β-oxidation-related genes were decreased in the obese mice after MC-LR exposure. Meanwhile, the protein expression levels of phosphorylation phosphatidylinositol 3-kinase (p-PI3K), phosphorylation protein kinase B (p-AKT), phosphorylation mammalian target of rapamycin (p-mTOR), and sterol regulatory element binding protein 1c (SREBP1-c) were increased; similarly, the p-PI3K/PI3K, p-AKT/AKT, p-mTOR/mTOR, and SREBP1/β-actin were significantly up-regulated in obese mice after being exposed to MC-LR, and the activated PI3K/AKT/mTOR/SREBP1 signaling pathway. In addition, MC-LR exposure reduced the activity of superoxide dismutase (SOD) and increased the level of malondialdehyde (MDA) in the obese mice's serum. In summary, the MC-LR could aggravate the HFD-induced obese mice liver lipid metabolism disorder by activating the PI3K/AKT/mTOR/SREBP1 signaling pathway to hepatocytes, increasing the SREBP1-c-regulated key enzymes for lipid synthesis, and blocking fatty acid β-oxidation.

Mussel-Inspired Surface Modification of α-Zirconium Phosphate Nanosheets for Anchoring Efficient and Reusable Ultrasmall Au Nanocatalysts

The shortage of powerful functionalities on scalable α-zirconium phosphate (ZrP) materials blocks the facile preparation of highly dispersed and immobilized metal nanocatalysts. We herein present a mild and facile mussel-inspired strategy based on polydopamine (PDA) for the surface modification of ZrP, and hence, the generation of powerful functionalities at a high density for the straightforward reduction of chloroauric acid to Au nanoparticles (AuNPs) and the immobilization of AuNPs. The resulting ternary ZrP@PDA/Au exhibited ultra-small AuNPs with a particle size of around 6.5 nm, as estimated based on TEM images. Consequently, the ZrP@PDA/Au catalyst showed significant activity in the catalytic conversion of 4-nitrophenol (4NP) to 4-aminophenol (4AP), a critical transformation reaction in turning the hazard into valuable intermediates for drug synthesis. The PDA was demonstrated to play a critical role in the fabrication of the highly efficient ZrP@PDA/Au catalyst, far outperforming the ZrP/Au counterpart. The turnover frequency (TOF) achieved by the ZrP@PDA/Au reached as high as 38.10 min^-1, much higher than some reported noble metal-based catalysts. In addition, the ZrP@PDA/Au showed high stability and reusability, of which the catalytic efficiency was not significantly degraded after prolonged storage in solution.

Examination of Microcystin Adsorption by the Type of Plastic Materials Used during the Procedure of Microcystin Analysis

The incidence of eutrophication is increasing due to fertilizer abuse and global warming. Eutrophication can induce the proliferation of cyanobacteria such as Microcystis, which produces microcystins. Microcystins are toxic to specific organs such as the liver and the heart. Thus, monitoring of microcystins is strongly required to control drinking water and agricultural product qualities. However, microcystins could be adsorbed by plastic materials during sample storage and preparation, hindering accurate analysis. Therefore, the current study examined the recovery rate of microcystins from six plastics used for containers and eight plastics used for membrane filters. Among the six plastics used for containers, polyethylene terephthalate showed the best recovery rate (≥81.3%) for 48 h. However, polypropylene, polystyrene, and high- and low-density polyethylenes showed significant adsorption after exposure for 1 hr. For membrane materials, regenerated cellulose (≥99.3%) showed the highest recovery rate of microcystins, followed by polyvinylidene fluoride (≥94.1%) and polytetrafluoroethylene (≥95.7%). The adsorption of microcystins appeared to be strongly influenced by various molecular interactions, including hydrophobic interaction, hydrogen bonding, and electrostatic interaction. In addition, microcystins’ functional residues seemed to be critical factors affecting their adsorption by plastic materials. The present study demonstrates that polyethylene terephthalate and regenerated cellulose membrane are suitable plastic materials for the analysis of microcystins.