Hydrogen peroxide induces apoptotic-like cell death in Microcystis aeruginosa (Chroococcales, Cyanobacteria) in a dose-dependent manner

We investigated the capability of Microcystis aeruginosa to cause apoptosis by pursuing morphological, molecular and physiological characteristics after exposure to H2O2. Microcystis proliferation was only weakly affected after exposure to 150 mu M H2O2 but cell numbers decreased dramatically after exposures of 250 and 325 mu M H2O2. Cells exposed to 250 and 325 mu M H2O2 were examined using transmission electron microscopy, and they exhibited membrane deformation and partial disintegration of thylakoids. Correspondingly, fluorescence imaging of DNA by Hoechst 33342 staining revealed the condensation of nucleoid chromatin. Moreover, cellular injury was concomitant with dramatic decreases in photosynthetic efficiency (ratio of variable fluorescence to maximum fluorescence [Fv/Fm], maximum electron transport rate [ETRmax]) and elevated caspase-3-like activity after exposure of 250 and 325 mu M H2O2. Terminal deoxynucleotidyl transferase Deoxyuridine 5-triphosphate nick end labelling (TUNEL) positive staining appeared in cells exposed to 250 mu M and 325 mu M H2O2, and the percentage staining increased with increasing H2O2 concentration. These data suggested that M. aeruginosa exposed to H2O2 underwent an apoptotic event. Additionally, cells exposed to H2O2 had increased cytoplasmic vacuolation and nontypical DNA laddering. Increased caspase-3-like activity was not inhibited in the presence of the synthetic caspase inhibitor carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone. Therefore, H2O2 induced apoptotic-like cell death in a dose-dependent manner. Taken together, our results provided a novel mechanism for explaining cyanobacterial bloom dynamics in response to environmental stress. The results also contributed to the understanding of the origin and evolution of programmed cell death.We investigated the capability of Microcystis aeruginosa to cause apoptosis by pursuing morphological, molecular and physiological characteristics after exposure to H2O2. Microcystis proliferation was only weakly affected after exposure to 150 mu M H2O2 but cell numbers decreased dramatically after exposures of 250 and 325 mu M H2O2. Cells exposed to 250 and 325 mu M H2O2 were examined using transmission electron microscopy, and they exhibited membrane deformation and partial disintegration of thylakoids. Correspondingly, fluorescence imaging of DNA by Hoechst 33342 staining revealed the condensation of nucleoid chromatin. Moreover, cellular injury was concomitant with dramatic decreases in photosynthetic efficiency (ratio of variable fluorescence to maximum fluorescence [Fv/Fm], maximum electron transport rate [ETRmax]) and elevated caspase-3-like activity after exposure of 250 and 325 mu M H2O2. Terminal deoxynucleotidyl transferase Deoxyuridine 5-triphosphate nick end labelling (TUNEL) positive staining appeared in cells exposed to 250 mu M and 325 mu M H2O2, and the percentage staining increased with increasing H2O2 concentration. These data suggested that M. aeruginosa exposed to H2O2 underwent an apoptotic event. Additionally, cells exposed to H2O2 had increased cytoplasmic vacuolation and nontypical DNA laddering. Increased caspase-3-like activity was not inhibited in the presence of the synthetic caspase inhibitor carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone. Therefore, H2O2 induced apoptotic-like cell death in a dose-dependent manner. Taken together, our results provided a novel mechanism for explaining cyanobacterial bloom dynamics in response to environmental stress. The results also contributed to the understanding of the origin and evolution of programmed cell death

An in vivo animal study assessing long-term changes in hypothalamic cytokines following perinatal exposure to a chemical mixture based on Arctic maternal body burden

Abstract Background The geographic distribution of environmental toxins is generally not uniform, with certain northern regions showing a particularly high concentration of pesticides, heavy metals and persistent organic pollutants. For instance, Northern Canadians are exposed to high levels of persistent organic pollutants like polychlorinated biphenyls (PCB), organochlorine pesticides (OCs) and methylmercury (MeHg), primarily through country foods. Previous studies have reported associations between neuronal pathology and exposure to such toxins. The present investigation assessed whether perinatal exposure (gestation and lactation) of rats to a chemical mixture (27 constituents comprised of PCBs, OCs and MeHg) based on Arctic maternal exposure profiles at concentrations near human exposure levels, would affect brain levels of several inflammatory cytokines Methods Rats were dosed during gestation and lactation and cytokine levels were measured in the brains of offspring at five months of age. Hypothalamic cytokine protein levels were measured with a suspension-based array system and differences were determined using ANOVA and post hoc statistical tests. Results The early life PCB treatment alone significantly elevated hypothalamic interleukin-6 (IL-6) levels in rats at five months of age to a degree comparable to that of the entire chemical mixture. Similarly, the full mixture (and to a lesser degree PCBs alone) elevated levels of the pro-inflammatory cytokine, IL-1b, as well as the anti-inflammatory cytokine, IL-10. The full mixture of chemicals also moderately increased (in an additive fashion) hypothalamic levels of the pro-inflammatory cytokines, IL-12 and tumor necrosis factor (TNF-α). Challenge with bacterial endotoxin at adulthood generally increased hypothalamic levels to such a degree that differences between the perinatally treated chemical groups were no longer detectable. Conclusions These data suggest that exposure at critical neurodevelopmental times to environmental chemicals at concentrations and combinations reflective of those observed in vulnerable population can have enduring consequences upon cytokines that are thought to contribute to a range of pathological states. In particular, such protracted alterations in the cytokine balance within the hypothalamus would be expected to favor marked changes in neuro-immune and hormonal communication that could have profound behavioral consequences.</p

Distribution and population dynamics of potential anatoxin-a-producing cyanobacteria in Lake Dianchi, China

The occurrence of cyanobacterial blooms is often accompanied by a variety of toxic secondary metabolites known as cyanotoxins. Anatoxin-a (ATX-a) is a highly toxic cyanobacterial neurotoxin synthesized by numerous species (e.g., Aphanizomenon, Anabaena and Oscillatoria) that has received much public attention. In this study, we used molecular methods (PCR and qPCR) to track the presence and dynamics of ATX-a-producing cyanobacteria, Aphanizomenon and Anabaena in Lake Dianchi, China based on the anaC and cpcBA-IGS genes over a 23-month period (from June 2010 to April 2012). Results revealed that Aphanizomenon was the major potential ATX-a producer in Lake Dianchi and that they were most abundant in early spring and least abundant in summer, coinciding with observed Aphanizomenon blooms. It was found that the proportion of ATX-a toxigenic cells was lower in the northern part of the lake (2.1%) than the middle (16.7%) and southern parts (19.2%). The information on the spatio-temporal distributions of ATX-a-producing cyanobacteria obtained in this study will help to build management strategies to improve water quality for public health. (C) 2015 Elsevier B.V. All rights reserved

Dynamic Analysis and Fault Diagnosis for Gear Transmission of a Vibration Exciter of a Mine-Used Vibrating Screen under Different Conditions

The helical gear pair of a box-type vibration exciter of a mine-used linear vibrating screen is subjected to complex excitation and prone to broken tooth failures. At present, investigation regarding the difference and particularity between gear transmission in vibrating screens (i.e., vibration machinery) and that in rotating machinery is still a challenge, which is the key to revealing the performance and failure mechanism of gear transmission in the premise of application to vibrating screens. In order to intuitively display the peculiarity of gear transmission on the exciter, an innovative virtual prototype model of a gear pair of a vibrating screen exciter is proposed. This model considers the effects of internal and external excitation, such as the friction and lubrication of the gear, strong alternating load produced by a large eccentric block, the reciprocating motion of the screen body, the large clearance of bearing and so on, and its correctness is verified. Based on the comparison, the inducement for the high fatigue rate of exciter gears is revealed. Models of a vibrating screen’s excitation system with different degrees of broken teeth are also established, and tooth fault features are proposed for fault detection. Sensitive indicators for the degradation degree of tooth damage are put forward, and the monitoring strategy is presented that with the increase of damage degree, the waveform index and pulse index of axial vibration acceleration increase. The analysis results provide powerful support for the optimal design of the vibrating screen’s exciter gears and fault diagnosis

Survival, recovery and microcystin release of Microcystis aeruginosa in cold or dark condition

Microcystis often dominates phytoplankton in eutrophic lakes and must survive a long period of cold or dark conditions. However, the survival strategies of Microcystis to withstand cold or dark stress are less well known. In this study, we conducted experiments on the responses of two toxic Microcystis aeruginosa strains (FACHB-905 and FACHB-915) and their microcystin release in conditions of low temperature (15 degrees C or 4 degrees C, with illumination) or darkness, and subsequent recovery in standard conditions (25 degrees C with illumination). On exposure to 15 degrees C, a small decrease in cell viability was observed, but the cell number increased gradually, suggesting that M. aeruginosa FACHB-905 and FACHB-915 cells seem in general tolerant in 15 degrees C. Interestingly, our results show that a higher carotenoid content and microcystin release potentially enhance the fitness of surviving cells at 15 degrees C. M. aeruginosa cells exposed to lower temperature light stress (4 degrees C) did not completely lose viability and retained the ability to reinitiate growth. In darkness, the maximum quantum yield (F-v/F-m) and the maximum electron transport rate (ETRmax) values and cell viability of M. aeruginosa cells gradually decreased with time. During the recovery period, the photosynthetic efficiency of M. aeruginosa reverted to the normal level. Additionally, M. aeruginosa FACHB-905 and FACHB-915 exposed to low temperature had increased caspase-3-like activity and DNA fragmentation, which suggests the occurrence of a type of cell death in M. aeruginosa cells under cold stress similar to programmed cell death. Overall, our findings could confer certain advantages on the Microcystis for surviving cold or dark conditions encountered in the annual cycle, and help explain its repeated occurrence in water blooms in large and shallow lakes.</p

Dynamic Analysis and Fault Diagnosis for Gear Transmission of a Vibration Exciter of a Mine-Used Vibrating Screen under Different Conditions

The helical gear pair of a box-type vibration exciter of a mine-used linear vibrating screen is subjected to complex excitation and prone to broken tooth failures. At present, investigation regarding the difference and particularity between gear transmission in vibrating screens (i.e., vibration machinery) and that in rotating machinery is still a challenge, which is the key to revealing the performance and failure mechanism of gear transmission in the premise of application to vibrating screens. In order to intuitively display the peculiarity of gear transmission on the exciter, an innovative virtual prototype model of a gear pair of a vibrating screen exciter is proposed. This model considers the effects of internal and external excitation, such as the friction and lubrication of the gear, strong alternating load produced by a large eccentric block, the reciprocating motion of the screen body, the large clearance of bearing and so on, and its correctness is verified. Based on the comparison, the inducement for the high fatigue rate of exciter gears is revealed. Models of a vibrating screen&rsquo;s excitation system with different degrees of broken teeth are also established, and tooth fault features are proposed for fault detection. Sensitive indicators for the degradation degree of tooth damage are put forward, and the monitoring strategy is presented that with the increase of damage degree, the waveform index and pulse index of axial vibration acceleration increase. The analysis results provide powerful support for the optimal design of the vibrating screen&rsquo;s exciter gears and fault diagnosis

The highly heterogeneous methylated genomes and diverse restriction-modification systems of bloom-forming Microcystis

The occurrence of harmful Microcystis blooms is increasing in frequency in a myriad of freshwater ecosystems. Despite considerable research pertaining to the cause and nature of these blooms, the molecular mechanisms behind the cosmopolitan distribution and phenotypic diversity in Microcystis are still unclear. We compared the patterns and extent of DNA methylation in three strains of Microcystis, PCC 7806SL, NIES-2549 and FACHB-1757, using Single Molecule Real-Time (SMRT) sequencing technology. Intact restriction-modification (R-M) systems were identified from the genomes of these strains, and from two previously sequenced strains of Microcystis, NIES-843 and TAIHU98. A large number of methylation motifs and R-M genes were identified in these strains, which differ substantially among different strains. Of the 35 motifs identified, eighteen had not previously been reported. Strain NIES-843 contains a larger number of total putative methyltransferase genes than have been reported previously from any bacterial genome. Genomic comparisons reveal that methyltransferases (some partial) may have been acquired from the environment through horizontal gene transfer. (C) 2018 Elsevier B.V. All rights reserved.</p

theecologicalrisksofhydrogenperoxideasacyanocideitseffectonthecommunitystructureofbacterioplankton

Microcystis blooms are an environmental and ecological concern that has received a serious attention. Hydrogen peroxide (H2O2) is an environment-friendly cyanocide that is commonly used to control Microcystis blooms. While the ecological safety of H2O2 has been previously studied, its influence on bacterioplankton has not been investigated to date. In this study, we used mesocosm experiments to determine the influence of H2O2 on the dynamic changes of the community structure of bacterioplankton. By using deep-sequencing and metagenomics strategy we determined the community structures of phytoplankton and bacterioplankton assemblages that were dominated by Microcystis at a highly eutrophic Dianchi Lake, China. The results showed that Microcystis was more sensitive to H2O2 than other eukaryotic algae. More interestingly, application of H(2)O(2 )changed the community structure of bacterioplankton, evidenced by the emergence of Firmicutes as the dominant species in place of Bacteroidetes and Proteobacteria. The H2O2 treatment resulted in the community of bacterioplankton that was primarily dominated by Exiguobacterium and Planomicrobium. Our results show that the abundance changed and the bacterioplankton diversity did not recover even after the concentration of H2O2 reached to the background level. Thus, the response of bacterioplankton must be considered when assessing the ecological risks of using H(2)O(2 )to control Microcystis blooms, because bacterioplankton is the key player that forms the basis of food web of aquatic environment