Whole-Genome Sequencing of Bacterial Isolates That Degrade the Cyanobacterial Toxin Microcystin-LR.
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ABSTRACT:
SUBMITTER: McCartney AT
PROVIDER: S-EPMC7530933 | biostudies-literature | 2020 Oct
REPOSITORIES: biostudies-literature
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Whole-Genome Sequencing of Bacterial Isolates That Degrade the Cyanobacterial Toxin Microcystin-LR.
McCartney Alexander T AT Yeo Ji-Youn JY Blomquist Thomas M TM Huntley Jason F JF
Microbiology resource announcements 20201001 40
We previously demonstrated that 13 bacterial isolates from Lake Erie, when grown in groups of four to five isolates per group, degraded the cyanobacterial toxin microcystin-LR (MC-LR) into nontoxic fragments. Whole-genome sequencing of these bacteria was performed to provide genus and species information and to predict putative MC-LR-degrading genes. ...[more]
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Project description:Microcystin-LR (MC-LR) is a cyclic hepatotoxin produced by cyanobacteria, including Microcystis sp. and Planktothrix sp. Harmful algal blooms (HABs) in Lake Erie have become a major human health concern in recent years, highlighted by the August 2014 city of Toledo, Ohio, municipal water "do not drink" order that affected nearly 500,000 residents for 3 days. Given that microcystin degrading bacteria have been reported from HAB-affected waters around the world, we hypothesized that MC-LR degrading bacteria could be isolated from Lake Erie. To test this hypothesis, 13 water samples were collected from various Lake Erie locations during the summers of 2014 and 2015, MC-LR was continuously added to each water sample for 3 to 5 weeks to enrich for MC-LR-degrading bacteria, and MC-LR was quantitated over time. Whereas MC-LR was relatively stable in sterile-filtered lake water, robust MC-LR degradation (up to 19 ppb/day) was observed in some water samples. Following the MC-LR selection process, 67 individual bacterial isolates were isolated from MC-LR degrading water samples and genotyped to exclude potential human pathogens, and MC-LR degradation by smaller groups of bacterial isolates (e.g., groups of 22 isolates, groups of 11 isolates, etc.) was examined. Of those smaller groups, selected groups of four to five bacterial isolates were found to degrade MC-LR into non-toxic forms and form robust biofilms on siliconized glass tubes. Taken together, these studies support the potential use of isolated bacterial isolates to remove MC-LR from drinking water.
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Project description:Cyanobacterial blooms have become more frequent and serious in recent years. Not only do massive blooms cause environmental pollution and nutrient eutrophication, but they also produce microcystins (MCs), a group of toxic cycloheptapeptides, which threaten aquatic ecosystem and human health. As such, clarifying the allelopathic interactions between cyanobacteria and other algae is critical to better understand the driving factors of blooms. To date, however, such studies remain largely insufficient. Here, we treated model alga Chlamydomonas reinhardtii with microcystin-LR (MC-LR) to determine its allelopathic effects. Results showed that MC-LR markedly suppressed C. reinhardtii cell viability. Comparative proteomic and physiological analyses revealed that MC-LR significantly up-regulated protein abundance of antioxidants ascorbate peroxidase (APX) and catalase (CAT) at the beginning stage of exposure. This was accompanied by an over-accumulation of hydrogen peroxide (H2O2), suggesting that MC-LR suppresses cell viability via oxidative damage. Furthermore, we found that MCs induced desulfhydrase (DES) activity for hydrogen sulfide (H2S) generation at the beginning stage. Additional H2S donors reactivated antioxidant enzyme activity, which reduced H2O2 accumulation and ultimately enhanced C. reinhardtii tolerance to MC-LR damage. This effect could be reserved by inhibiting H2S biosynthesis. Simultaneously, we found that H2S also suppressed MC-LR-induced cell autophagy, and thus attenuated the toxic effects of MC-LR. Our findings suggest that oxidative bursts may be the main reason for the allelopathic effects of MC-LR on C. reinhardtii viability and that H2S signaling may enhance C. reinhardtii tolerance to MC-LR through the activation of antioxidant enzyme activity and suppression of cell autophagy.
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Project description:BackgroundCyanobacterial harmful algal blooms (CyanoHABs) originate from the excessive growth or bloom of cyanobacteria often referred to as blue-green algae. They have been on the rise globally in both marine and freshwaters in recently years with increasing frequency and severity owing to the rising temperature associated with climate change and increasing anthropogenic eutrophication from agricultural runoff and urbanization. Humans are at a great risk of exposure to toxins released from CyanoHABs through drinking water, food, and recreational activities, making CyanoHAB toxins a new class of contaminants of emerging concern.ObjectivesWe investigated the toxic effects and mechanisms of microcystin-LR (MC-LR), the most prevalent CyanoHAB toxin, on the ovary and associated reproductive functions.MethodsMouse models with either chronic daily oral or acute intraperitoneal exposure, an engineered three-dimensional ovarian follicle culture system, and human primary ovarian granulosa cells were tested with MC-LR of various dose levels. Single-follicle RNA sequencing, reverse transcription-quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, western blotting, immunohistochemistry (IHC), and benchmark dose modeling were used to examine the effects of MC-LR on follicle maturation, hormone secretion, ovulation, and luteinization.ResultsMice exposed long term to low-dose MC-LR did not exhibit any differences in the kinetics of folliculogenesis, but they had significantly fewer corpora lutea compared with control mice. Superovulation models further showed that mice exposed to MC-LR during the follicle maturation window had significantly fewer ovulated oocytes. IHC results revealed ovarian distribution of MC-LR, and mice exposed to MC-LR had significantly lower expression of key follicle maturation mediators. Mechanistically, in both murine and human granulosa cells exposed to MC-LR, there was reduced protein phosphatase 1 (PP1) activity, disrupted PP1-mediated PI3K/AKT/FOXO1 signaling, and less expression of follicle maturation-related genes.DiscussionUsing both in vivo and in vitro murine and human model systems, we provide data suggesting that environmentally relevant exposure to the CyanoHAB toxin MC-LR interfered with gonadotropin-dependent follicle maturation and ovulation. We conclude that MC-LR may pose a nonnegligible risk to women's reproductive health by heightening the probability of irregular menstrual cycles and infertility related to ovulatory disorders. https://doi.org/10.1289/EHP12034.
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