Comparative metabolomic analysis of exudates of microcystin-producing and microcystin-free Microcystis aeruginosa strains

Cyanobacterial harmful algal blooms (cHABs) dominated by Microcystis aeruginosa threaten the ecological integrity and beneficial uses of lakes globally. In addition to producing hepatotoxic microcystins (MC), M. aeruginosa exudates (MaE) contain various compounds with demonstrated toxicity to aquatic biota. Previously, we found that the ecotoxicity of MaE differed between MC-producing and MC-free strains at exponential (E-phase) and stationary (S-phase) growth phases. However, the components in these exudates and their specific harmful effects were unclear. In this study, we performed untargeted metabolomics based on liquid chromatography-mass spectrometry to reveal the constituents in MaE of a MC-producing and a MC-free strain at both E-phase and S-phase. A total of 409 metabolites were identified and quantified based on their relative abundance. These compounds included lipids, organoheterocyclic compounds, organic acid, benzenoids and organic oxygen compounds. Multivariate analysis revealed that strains and growth phases significantly influenced the metabolite profile. The MC-producing strain had greater total metabolites abundance than the MC-free strain at S-phase, whereas the MC-free strain released higher concentrations of benzenoids, lipids, organic oxygen, organic nitrogen and organoheterocyclic compounds than the MC-producing strain at E-phase. Total metabolites had higher abundance in S-phase than in E- phase in both strains. Analysis of differential metabolites (DMs) and pathways suggest that lipids metabolism and biosynthesis of secondary metabolites were more tightly coupled to growth phases than to strains. Abundance of some toxic lipids and benzenoids DMs were significantly higher in the MC-free strain than the MC-producing one. This study builds on the understanding of MaE chemicals and their biotoxicity, and adds to evidence that non-MC-producing strains of cyanobacteria may also pose a threat to ecosystem health

Comparative feeding rates of native and invasive ascidians

Ascidians have a recent history of species introductions globally, often with strong ecological impacts. Comparisons of per capita effects of invaders and comparable natives are useful to assess such impacts. Here, we explore ingestion rates (IR) and clearance rates (CR) of Ciona intestinalis and Ciona robusta, co-occurring native and non-native ascidians, respectively, from Brittany, France. IR was positively related to food concentration, with the invader responding more strongly to increasing food concentration. CR also differed by species, with the invader demonstrating higher values. C. robusta exhibited a higher functional response (Type I) than did C. intestinalis (Type II). Relative impact measured using seasonal abundance and IR revealed that C. robusta has a much greater impact than C. intestinalis at all food concentrations tested, though the former has a constrained distribution which limits its regional impact. Nevertheless, when abundant, we expect C. robusta to exert a greater impact on algal foods

Comparative metabolomics of exudates between toxigenic and non-toxigenic Microcystis aeruginosa

Cyanobacterial Harmful Algal Blooms (CHABs, dominated by Microcystis aeruginosa) have received high attention for decades owing to the noxious and harmful secondary metabolites and toxins that they produce and release upon into water. Research on the active components and future risk assessment of them are demanded. M. aeruginosa strains could be characterized as ‘toxigenic’ (genomics containing mcy gene) or ‘non-toxigenic’ (genomics not containing mcy gene), according to whether they produce microcystins or not. We employed nontargeted metabolomics technique to compare components and their abundances in exudates from toxigenic M. aeruginosa strain (FACHB-905) and non-toxigenic strain (FACHB-526) at exponential and stationary growth stages. In total, 409 metabolites were identified and lipids, organoheterocyclic compounds and benzenoids were found with high abundances. The two strains in the same growth stage had similar metabolites, but more metabolites were accumulated at stationary phase than exponential stage. Although FACHB-905 exudated more metabolites than FACHB-526, some known bioactive and toxic metabolites, e.g. 7-ketocholesterol, glyceraldehyde and myristoleic acid, were significantly accumulated higher in FACHB-526 exudates. Our results would be valuable for further risk prediction of cyanobacterial booms, especially for the non-toxigenic strains, and healthy water management

Revising Yield and Equivalence Factors of Ecological Footprints Based on Land-Use Conversion

In the current ecological footprint (EF) calculations, the parameters of built-up land are set as equal to those of cropland, based on the assumption that built-up land is totally converted from cropland. However, built-up land may be derived from other types of land use. With the expansion of built-up area as a result of urbanization, the yield and equivalence factors of built-up land are becoming increasingly important in the EF calculation. The objective of this study was to evaluate the influence of this assumption on EF calculation. In this study, the proportions of different land types converted into built-up land were evaluated based on actual land-use conversion in two urbanized areas of Yunnan Province and Kunming City from 1980 to 2010 in the ArcGIS platform. Then, the parameters of built-up land were calculated by an area-weighting approach with the proportions. The results showed the following: (1) In both cases, the EF of Yunnan Province and Kunming City were greater than their biocapacities (BC), indicating that they were in unsustainable states. (2) The EF and BC of the two studied cases were reduced to varying degrees because the yield and equivalence factors of built-up land from land-use conversion are less than cropland factors. As the proportion of the built-up land area in Kunming City was larger than that in Yunnan Province, the reduced proportion of the EF and BC of Kunming City is greater than that of Yunnan Province. (3) The proportion of built-up land converted from cropland has a significantly positive correlation with EF and BC. Therefore, it is of great significance to revise the yield and equivalence factors of built-up land using actual land-use conversions in highly urbanized areas

Effects of Cyanobacterial Secondary Metabolites on Phytoplankton Community Succession

Allelopathic effects are one of the factors potentially influencing the succession ofphytoplankton communities; however, their influence has often been neglected.This is especially true for cyanobacteria that often outcompete other phytoplanktonspecies and form blooms causing severe problems. Allelopathic effects ofcyanobacteria can play an important role for phytoplankton succession. In thischapter, we introduce the different ways how aquatic organisms are influenced bycyanobacterial allelochemicals; the mechanisms of their interaction from the aspects of chemical intermediates, target reaction, and target signals; and interferingfactors and the ecological consequences of this process.Cyanobacteria produce and excrete a variety of allelopathic compounds thataffect other Cyanophyta, eukaryotic algae, bacteria, zooplankton, higher plants,and fish and mammalian cells. These effects are regulated by various abiotic andbiotic conditions, such as nutrient availability, temperature, and light intensity butalso cell density and growth phase of the source cyanobacterial community. Thebioactive metabolites include cyclic peptides, alkaloids, terpenoids, and otherswhich can have a variety of inhibitory effects on the different target organisms.Ecological consequences such as declines in biodiversity and accumulation oftoxins in the food chain have been shown. However, most of these compoundshave not yet been fully tested regarding their full range of effects on naturalphytoplankton communities. A detailed elucidation of the influence ofcyanobacterial allelochemicals is of key importance for understanding and managingthe succession of natural phytoplankton communities

Varying hydrological response to climate change in three neighborhood plateau lake basins: Localized climate change feature matters

Climate change and its impact on plateau lakes are of wide concern in China owing to their diverse yet fragile ecosystems. The three largest and most concerning plateau lakes (Dianchi, Erhai, and Fuxian lakes) in southwestern China were selected as case studies to demonstrate their different hydrological responses attributing to the local climatic and watershed characteristics. We processed 27 climate change scenarios according to the local climate characteristics and simulated the daily runoff of each lake basin under the historical and the 27 climate change scenarios. Then we analyzed the change of mean annual and seasonal runoff, and hydrological extremes of each lake basin. The results indicate a great risk of socio-economic and ecological for these plateau lakes as climate change will significantly alter the horological regimes of each lake basin. The mean annual runoff of the three lake basins will change from–65.24 to 54.17 %, when the air temperature increases by 1–2 °C and precipitation changes from –20 to + 20 %. Climatic and topographic heterogeneities caused each lake basin responded differently to climate change. Among them, the LFB was more sensitive to climate change than the LDB and LEB. Changes in the annual and seasonal runoff for the LFB were approximately 1.5-fold higher than that of the LDB and LEB. The hydrological extremes in the LFB also had the most significant changes. To cope with future climate change, each lake requires reasonable and effective mitigation measures

Phytosphingosine inhibits cell proliferation by damaging DNA in human cell lines

Harmful cyanobacterial blooms have caused numerous biosecurity incidents owing to the production of hazardous secondary metabolites such as microcystin. Additionally, cyanobacteria also release many other components that have not been explored. We identified compounds of a toxic mixture exudated from a dominant, blooming species, Microcystis aeruginosa, and found that phytosphingosine (PHS) was one of the bioactive components. Since PHS exhibited toxicity and is deemed a hazardous substance by the European Chemicals Agency, we hypothesized that PHS is a potentially toxic compound in M. aeruginosa exudates. However, the mechanisms of PHS ecotoxicity remain unclear. We assessed the cytotoxicity of PHS using an in vitro cell model in eight human cell lines and observed that the nasopharyngeal carcinoma cell line CNE2 was the most sensitive. We exposed CNE2 cells to 0–25 µmol/L PHS for 24 hr to explore its toxicity and mechanism. PHS exposure resulted in abnormal nuclear morphology, micronuclei, and DNA damage. Moreover, PHS significantly inhibited cell proliferation and arrested cell cycle at S phase. The results of Western blot suggested that PHS increased the expression of DNA damage-related proteins (ATM, p-P53 and P21) and decreased the expression of S phase-related proteins (CDK2, CyclinA2 and CyclinE1), indicating the toxicological mechanism of PHS on CNE2 cells. These data provide evidence that PHS has genetic toxicity and inhibits cell proliferation by damaging DNA. Our study provides evidence that PHS inhibits cell proliferation by damaging DNA. While additional work is required, we propose that PHS been considered as a potentially toxic component in MaE in addition to other well-characterized secondary compounds

Cyanobacteria blooms induce embryonic heart failure in an endangered fish species

Cyanobacterial blooms drive water-quality and aquatic-ecosystem deterioration in eutrophic lakes worldwide, mainly owing to their harmful, secondary metabolites. The response of fish exposed to these cyanobacterial chemicals, however, remains largely unknown. In this paper, we employed an endangered fish species (Sinocyclocheilus grahami) in Dianchi Lake, China to evaluate the risks of cell-free exudates (MaE) produced by a dominant cyanobacterium (Microcystis aeruginosa) on embryo development, as well as the molecular mechanisms responsible. MaE (3d cultured) caused a reduction of fertilization (35.4%) and hatching (15.5%) rates, and increased mortality rates (≤90.0%) and malformation rate (27.6%), typically accompanied by heart failure. Proteomics analysis revealed that two greatest changed proteins – protein S100A1 (over-expressed 26 times compared with control) and myosin light chain (under-expressed 25 fold) – are closely associated with heart function. Further study revealed that heart failure was due to calcium ion imbalance and malformed cardiac structure. We conclude that harmful secondary metabolites from cyanobacteria may adversely affect embryo development in this endangered fish, and possibly contribute to its disappearance and unsuccessful recovery in Dianchi Lake. Hazardous consequences of substances released by cyanobacteria should raise concerns for managers addressing recovery of this and other imperiled species in affected lakes

Data from: Comparative feeding behaviour of native and introduced terrestrial snails tracks their ecological impacts

A developing body of theory and empirical evidence suggest that feeding behaviour as measured by the functional response (FR) can assist researchers in assessing the relative potential ecological impacts and competitive abilities of native and introduced species. Here, we explored the FRs of two land snails that occur in SW Ontario, one native (Mesodon thyroidus) and one non-indigenous (Cepaea nemoralis) to Canada. The non-indigenous species appears to have low ecological impact and inferior competitive abilities. Consistent with theory, while both species conformed to Type II functional responses, the native species had a significantly higher attack rate (5.30 vs 0.41, respectively) and slightly lower handling time (0.020 vs. 0.023), and hence a higher maximum feeding rate (50.0 vs 43.5). The non-indigenous species exhibited a significantly longer time to contact for a variety of food types, and appeared less discriminating of paper that was offered as a non-food type. The non-indigenous species also ate significantly less food when in mixed species trials with the native snail. These feeding patterns match the known low ecological impact of the introduced snail and are consistent with the view that it is an inferior competitor relative to the native species. However, field experimentation is required to clarify whether the largely microallopatric distributions of the two species in SW Ontario reflect competitive dominance by the native species or other factors such as habitat preference, feeding preferences or predator avoidance. The relative patterns of feeding behaviour and ecological impact are, however, fully in line with recent functional response theory and application

Functional response (consumption data) of Mesodon thyroidus

Raw consumption data of M. thyroidus individuals used for generating functional response curves and analyzing 'a' and 'h' parameters