Colony formation is an essential stage of cyanobacterial blooms. High calcium concentration can promote Microcystis aeruginosa aggregation behavior, but the mechanism of colony formation caused by calcium has rarely been reported. In this study, high calcium-induced colony formation was identified as a shift from cell adhesion to cell division, rather than only cell adhesion as previously thought. Algae responded to this calcium-induced environmental pressure by aggregating and forming colonies. Algal cells initially secreted large quantities of extracellular polysaccharides (EPS) and rapidly aggregated by cell adhesion. The highest aggregation proportion was up to 68.93%. However, high calcium concentrations cannot completely inhibit algal cell growth, but only delay the algae into the rapid growth phase. With adaption to calcium and existing high EPS content, the daughter cells reduced EPS synthesis and the aggregation proportion decreased. The increasing growth rate was also responsible for the decreased xylose content in EPS. The mechanism of colony formation changed to cell division. The downregulation of genes related to EPS secretion also supported this hypothesis. Overall, these results can benefit for our understanding of cyanobacterial bloom formation.

Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are two widely used polyfluorinated compounds (PFCs) and are persistent in the environment. This study for the first time systematically investigated their toxicities and the underlying mechanisms to Escherichia coli. Much higher toxicity was observed for PFOA than PFOS, with the 3 h half growth inhibition concentrations (IC50) determined to be 10.6 ± 1.0 and 374 ± 3 mg L−1, respectively, while the bacterial accumulation of PFOS was much greater than that of PFOA. The PFC exposures disrupted cell membranes as evidenced by the dose-dependent variations of cell structures (by transmission electron microscopy observations), surface properties (electronegativity, hydrophobicity, and membrane fluidity), and membrane compositions (by gas chromatogram and Fourier transform infrared spectroscopy analyses). The increases in the contents of intracellular reactive oxygen species (ROS) and malondialdehyde and the activity of superoxide dismutase indicated the increment of oxidative stress induced by the PFCs in the bacterial cells. The fact that the cell growth inhibition was mitigated by the addition of ROS scavenger (N-acetyl cysteine) further evidenced the important role of oxidative damage in the toxicities of PFOS and PFOA. Eighteen genes involved in cell division, membrane instability, oxidative stress, and DNA damage of the exposed cells were up or down expressed, indicating the DNA damage by the PFCs. The toxicities of PFOS and PFOA to E. coli were therefore ascribed to the membrane disruption, oxidative stress, and DNA damage induced cell inactivation and/or death. The difference in the bactericidal effect between PFOS and PFOA was supposed to be related to their different dominating toxicity mechanisms, i.e., membrane disruption and oxidative damage, respectively. The outcomes will shed new light on the assessment of ecological effects of PFCs.

Polycyclic aromatic hydrocarbons (PAHs), ubiquitous organic pollutants in the environment, can accumulate in humans via the food chain and then harm human health. MiRNAs (microRNAs), a kind of non-coding small RNAs with a length of 18–30 nucleotides, regulate plant growth and development and respond to environmental stress. In this study, it is demonstrated that miR164 can regulate root growth and adventitious root generation of wheat under phenanthrene exposure by targeting NAC (NAM/ATAF/CUC) transcription factor. We observed that phenanthrene treatment accelerated the senescence and death of wheat roots, and stimulated the occurrence of new roots. However, it is difficult to compensate for the loss caused by old root senescence and death, due to the slower growth of new roots under phenanthrene exposure. Phenanthrene accumulation in wheat roots caused to generate a lot of reactive oxygen species, and enhanced lipoxygenase activity and malonaldehyde concentration, meaning that lipid peroxidation is the main reason for root damage. MiR164 was up-regulated by phenanthrene, enhancing the silence of NAC1, weakening the association with auxin signal, and inhibiting the occurrence of adventitious roots. Phenanthrene also affected the expression of CDK (the coding gene of cyclin-dependent kinase) and CDC2 (a gene regulating cell division cycle), the key genes in the cell cycle of pericycle cells, thereby affecting the occurrence and growth of lateral roots. In addition, NAM (a gene regulating no apical meristem) and NAC23 may also be related to the root growth and development in wheat exposed to phenanthrene. These results provide not only theoretical basis for understanding the molecular mechanism of crop response to PAHs accumulation, but also knowledge support for improving phytoremediation of soil or water contaminated by PAHs.

Cylindrospermopsin (CYN) is an emerging cyanotoxin increasingly being found in freshwater cyanobacterial blooms worldwide. Humans and animals are exposed to CYN through the consumption of contaminated water and food as well as occupational and recreational water activities; therefore, it represents a potential health threat. It exhibits genotoxic effects in metabolically active test systems, thus it is considered as pro-genotoxic. In the present study, the advanced 3D cell model developed from human hepatocellular carcinoma (HepG2) cells was used for the evaluation of CYN cyto-/genotoxic activity. Spheroids were formed by forced floating method and were cultured for three days under static conditions prior to exposure to CYN (0.125, 0.25 and 0.5 μg/mL) for 72 h. CYN influence on spheroid growth was measured daily and cell survival was determined by MTS assay and live/dead staining. The influence on cell proliferation, cell cycle alterations and induction of DNA damage (γH2AX) was determined using flow cytometry. Further, the expression of selected genes (qPCR) involved in the metabolism of xenobiotics, proliferation, DNA damage response, apoptosis and oxidative stress was studied. Results revealed that CYN dose-dependently reduced the size of spheroids and affected cell division by arresting HepG2 cells in G1 phase of the cell cycle. No induction of DNA double strand breaks compared to control was determined at applied conditions. The analysis of gene expression revealed that CYN significantly deregulated genes encoding phase I (CYP1A1, CYP1A2, CYP3A4, ALDH3A) and II (NAT1, NAT2, SULT1B1, SULT1C2, UGT1A1, UGT2B7) enzymes as well as genes involved in cell proliferation (PCNA, TOP2α), apoptosis (BBC3) and DNA damage response (GADD45a, CDKN1A, ERCC4). The advanced 3D HepG2 cell model due to its more complex structure and improved cellular interactions provides more physiologically relevant information and more predictive data for human exposure, and can thus contribute to more reliable genotoxicity assessment of chemicals including cyanotoxins.

Microalgae are commonly used in ecotoxicity testing due to their ease of culturing and rapid cell division rates. These tests generally utilise a single species of algae; however, microalgae occur in the environment as complex communities of multiple species. To date, routine multispecies toxicity tests using tropical microalgae have not been available. This study investigated four tropical freshwater microalgal species for use in a chronic multispecies toxicity test based on the population growth (cell division) rate: Pediastrum duplex, Monoraphidium arcuatum, Nannochloropsis-like sp. and Chlorella sp. 12. Flow cytometric analysis identified the different fluorescence and light scattering properties of each algal species and quantified each species within multispecies mixtures. Following optimisation of test media nutrients and pH, a toxicity testing protocol was developed with P. duplex, M. arcuatum and Nannochloropsis-like sp. There were no significant differences in growth rates of each alga when tested over 72 h as single species or in multispecies mixtures. Atrazine and imazapic, two herbicides with different modes of action, were used to assess the sensitivity of the multispecies toxicity test. Atrazine was toxic to all species with 72-h IC10 values of 7.2, 63 and 280 μg/L for P. duplex, M. arcuatum and Nannochloropsis-like sp. respectively, while imazapic was not toxic to any species at concentrations up to 1100 μg/L. The toxicity of atrazine and imazapic to each microalgal species in the multispecies toxicity test was the same as that determined from single-species toxicity tests indicating that the presence of these microalgae in a mixture did not affect the toxicity of these two herbicides. This study is the first to develop a multispecies tropical microalgal toxicity test for application in freshwaters. This time- and cost-effective tool can be utilised to generate data to assist environmental decision making and to undertake risk assessments of contaminants in tropical freshwater environments.

Telomeres are non-coding DNA repeats located at the termini of eukaryotic chromosomes, regulated by dynamic processes balancing shortening and maintenance. Despite a mechanism to slow-down telomere shortening, cell division leads to progressive attrition of chromosomes, leading to the onset of cellular senescence or apoptosis. However, telomere restoration based on telomerase activity is the primary mechanism for telomere maintenance. Telomere length is associated to health and survival and can be impacted by a broad panel of environmental factors. However, the effect of contaminants on telomeres is poorly known for living organisms. The aim of this study was to investigate relationships between some poly- and perfluoroalkyl substances (PFASs), body condition and telomere length by using both a cross-sectional and longitudinal approach in adult breeding Black-legged kittiwakes (Rissa tridactyla) from Svalbard. First, we examined the associations between absolute telomere length and PFASs contamination in a given year (cross-sectional approach). Second, we investigated the relationships between telomere dynamics and PFASs contamination within a two years’ time frame (longitudinal approach). Our results did not show any significant relationships of PFASs and body condition with absolute telomere length in a given year. Surprisingly, we found a positive and significant relationship between PFASs and telomere dynamics in both sexes with elongated telomere in birds bearing the highest concentrations of PFASs. Our study underlines (i) the need to investigate PFAS effects on telomere dynamics with a longitudinal approach and (ii) a potential positive effect of these contaminants on telomere length, with the most contaminated birds showing the slowest rate of telomere shortening or even displaying elongated ones. Our study is the first to report a relationship between PFASs and telomere length in free-living vertebrates. A possible underlying mechanism and other potential confounding factors are discussed.

The effects of different copper concentrations on percentage germination, increase in fresh weight and radicle growth of Vicia sativa L. seeds were studied. Physiological studies showed that the germination rate was not affected up to a concentration of 5 × 10−3 M, but already at 10−3 M the copper stopped root elongation. Structural and ultrastructural observations of embryo and cotyledon reserve mobilization showed that inhibition of radicle growth at 10−3 M Cu concentration cannot be ascribed to nutrient shortage but probably to an effect of copper on radicle cell division and elongation. In seeds treated with 5 × 10−3 M CuBr2, the copper completely inhibited cotyledon protein mobilization, so that embryo protein mobilization supported normal growth of the radicle up to 30 h after imbibition. The particular protein content of adjacent cotyledon cells is also discussed.

Though the main toxic mechanisms of graphene oxide (GO) to algae have been accepted as the shading effect, oxidative stress and mechanical damage, the effect of algal characteristics on these three mechanisms of GO toxicity have seldom been taken into consideration. In this study, we investigated GO toxicity to green algae (Chlorella vulgaris, Scenedesmus obliquus, Chlamydomonas reinhardtii), cyanobacteria (Microcystis aeruginosa) and diatoms (Cyclotella sp.). The aim was to assess how the physiological characteristics of algae affect the toxicity of GO. Results showed that 10 mg/L of GO significantly inhibited the growth of all tested algal types, while S. obliquus and C. reinhardtii were found to be the most susceptible and tolerant species, respectively. Then, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the physiological characteristics of the assessed algae. The presence of locomotive organelles, along with smaller and more spherical cells, was more likely to alleviate the shading effect. Variations in cell wall composition led to different extents of mechanical damage as shown by Cyclotella sp. silica frustules and S. obliquus autosporine division being prone to damage. Meanwhile, growth inhibition and cell division were significantly correlated with the oxidative stress and membrane permeability, suggesting the latter two indicators can effectively signal GO toxicity to algae. The findings of this study provide novel insights into the toxicity of graphene materials in aquatic environments.

Bisphenol A (BPA) is a harmful environmental contaminant acting as an endocrine disruptor in animals, but it also affects growth and development in plants. Here, we have elucidated the functional mechanism of root growth inhibition by BPA in Arabidopsis thaliana using mutants, reporter lines and a pharmacological approach. In response to 10 ppm BPA, fresh weight and main root length were reduced, while auxin levels increased. BPA inhibited root growth by reducing root cell length in the elongation zone by suppressing expansin expression and by decreasing the length of the meristem zone by repressing cell division. The inhibition of cell elongation and cell division was attributed to the enhanced accumulation/redistribution of auxin in the elongation zone and meristem zone in response to BPA. Correspondingly, the expressions of most auxin biosynthesis and transporter genes were enhanced in roots by BPA. Taken together, it is assumed that the endocrine disruptor BPA inhibits primary root growth by inhibiting cell elongation and division through auxin accumulation/redistribution in Arabidopsis. This study will contribute to understanding how BPA affects growth and development in plants.

There has been an increasing incidence rate of rice false smut in global rice cultivation areas. However, there is a dearth of studies on the environmental concentrations and hazards of ustiloxin A (UA), which is the major mycotoxin produced by a pathogenic fungus of the rice false smut. Here, the concentrations of UA in the surface waters of two paddy fields located in Enshi city, Hubei province, China, were measured, and its toxicity in T. Thermophila was evaluated. This is the first study to detect UA in the surface waters of the two paddy fields, and the measured mean concentrations were 2.82 and 0.26 μg/L, respectively. Exposure to 2.19, 19.01 or 187.13 μg/L UA for 5 days significantly reduced the theoretical population and cell size of T. thermophila. Furthermore, treatment with 187.13 μg/L UA changed the percentages of T. thermophila cells in different cell-cycle stages, and with an increased malformation rate compared with the control, suggesting the disruption of the cell cycle. The expressions of 30 genes involved in the enriched proteasome pathway, 7 cyclin genes (cyc9, cyc10, cyc16, cyc22, cyc23, cyc26, cyc33) and 2 histone genes (mlh1 and hho1) were significantly down-regulated, which might be the modes of action responsible for the disruption of cell cycling due to UA exposure.