Effects of chlorinated benzenes on diatom fatty acid composition and quantitative morphology. IV. Pentachlorobenzene and comparison with trichlorobenzene isomers

Changes in the morphology and cell ultrastructure of a microalgal community exposed to a commercial glyphosate formulation and a toxigenic cyanobacterium

Human activities significantly influence the health of aquatic ecosystems because many noxious chemical wastes are discharged into freshwater bodies. Intensive agriculture contributes to the deterioration by providing indirectly fertilizers, pesticides, and other agrochemicals that affect the aquatic biota. Glyphosate is one of the most used herbicides worldwide, and microalgae are particularly sensitive to its formulation, inducing displacement of some green microalgae from the phytoplankton that leads to alterations in the floristic composition, which fosters the abundance of cyanobacteria, some of which can be toxigenic. The combination of chemical stressors such as glyphosate and biological ones, like cyanotoxins and other secondary metabolites of cyanobacteria, could induce a combined effect potentially more noxious to microalgae, affecting not only their growth but also their physiology and morphology. In this study, we evaluated the combined effect of glyphosate (Faena^®) and a toxigenic cyanobacterium on the morphology and ultrastructure of microalgae in an experimental phytoplankton community. For this purpose, Microcystis aeruginosa (a cosmopolitan cyanobacterium that forms harmful blooms) and the microalgae Ankistrodesmus falcatus, Chlorella vulgaris, Pseudokirchneriella subcapitata, and Scenedesmus incrassatulus were cultivated, individually and jointly, exposing them to sub-inhibitory concentrations of glyphosate (IC₁₀, IC_20, and IC₄₀). Effects were evaluated through scanning electron (SEM) and transmission electron (TEM) microscopy. Exposure to Faena^® produced alterations in the external morphology and ultrastructure of microalgae both individually and in combined cultures. SEM evidenced the loss of the typical shape and integrity of the cell wall and an increase in the biovolume. TEM revealed reduction and disorganization of the chloroplast, variation in starch and polyphosphate granules, formation of vesicles and vacuoles, cytoplasm degradation, and cell wall continuity loss. The presence of M. aeruginosa was, for microalgae, an additional stress factor adding to the chemical stress produced by Faena^®, increasing the damage in their morphology and ultrastructure. These results alert to the effects that can be caused by glyphosate and the presence of toxigenic bacteria on the algal phytoplankton in contaminated and anthropic and eutrophic freshwater ecosystems.

Occurrence of OCPs & PCBs and their effects on multitrophic biological communities in riparian groundwater of the Beiluo River, China

Persistent Organic Pollutants (POPs) may exert adverse effects on human and ecosystem health. However, as an ecologically fragile zone with strong interaction between river and groundwater, the POPs pollution in the riparian zone has received little attention. The goal of this research is to examine the concentrations, spatial distribution, potential ecological risks, and biological effects of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in the riparian groundwater of the Beiluo River, China. The results showed that the pollution level and ecological risk of OCPs in riparian groundwater of the Beiluo River were higher than PCBs. The presence of PCBs (Penta-CBs, Hexa-CBs) and CHLs, respectively, may have reduced the richness of bacteria (Firmicutes) and fungi (Ascomycota). Furthermore, the richness and Shannon's diversity index of algae (Chrysophyceae and Bacillariophyta) decreased, which could be linked to the presence of OCPs (DDTs, CHLs, DRINs), and PCBs (Penta-CBs, Hepta-CBs), while for metazoans (Arthropoda) the tendency was reversed, presumably as a result of SULPHs pollution. In the network analysis, core species belonging to bacteria (Proteobacteria), fungi (Ascomycota), and algae (Bacillariophyta) played essential roles in maintaining community function. Burkholderiaceae and Bradyrhizobium can be considered biological indicators of PCBs pollution in the Beiluo River. Note that the core species of interaction network, playing a fundamental role in community interactions, are strongly affected by POPs pollutants. This work provides insights into the functions of multitrophic biological communities in maintaining the stability of riparian ecosystems through the response of core species to riparian groundwater POPs contamination.

Impact of diuron and S-metolachlor on the freshwater diatom Gomphonema gracile: Complementarity between fatty acid profiles and different kinds of ecotoxicological impact-endpoints

Fatty acids (FA) are crucial for the maintenance of membrane fluidity and play a central role in metabolic energy storage. Polyunsaturated fatty acids play an essential ecological role since they are key parameters in the nutritional value of algae. Pesticide impacts on fatty acid profiles have been documented in marine microalgae, but remain understudied in freshwater diatoms. The aims of this study were to: 1) investigate the impact of diuron and S-metolachlor on "classical descriptors" (photosynthesis, growth rate, pigment contents, and on the expression levels of target genes in freshwater diatoms), 2) examine the impact of these pesticides on diatom fatty acid profiles and finally, 3) compare fatty acid profiles and "classical descriptor" responses in order to evaluate their complementarity and ecological role. To address this issue, the model freshwater diatom Gomphonema gracile was exposed during seven days to diuron and S-metolachlor at 10 μg.L^-1. G. gracile was mostly composed of the following fatty acids: 20:5n3; 16:1; 16:0; 16:3n4; 14:0 and 20:4n6 and highly unsaturated fatty acids were overall the best represented fatty acid class. S-metolachlor decreased the growth rate and chlorophyll a content of G. gracile and induced the expression of cox1, nad5, d1 and cat genes, while no significant impacts were observed on photosynthesis and carotenoid content. In a more global way, S-metolachlor did not impact the fatty acid profiles of G. gracile. Diuron inhibited photosynthesis, growth rate, chlorophyll a content and induced cat and d1 gene expressions but no significant effect was observed on carotenoid content. Diuron decreased the percentage of highly unsaturated fatty acids but increased the percentage of monounsaturated fatty acids. These results demonstrated that fatty acids responded to diuron conversely to pigment content, suggesting that fatty acids can inform on energy content variation in diatoms subjected to herbicide stress.

Embryos of an Antarctic zooplankton require anoxia for dormancy, are permeable to lipophilic chemicals, and reside in sediments containing PCBs

Zooplankton in Antarctic maritime lakes face challenges imposed by anthropogenic chemicals. Studies on temperate species suggest that lipophilic chemicals will accumulate in dormant embryos of Antarctic zooplankton and decrease hatching success, thereby threatening centuries of accumulated genetic diversity that would increase population resilience in the face of climate change. We evaluated the potential for lakes to act as sinks for legacy pollutants in the maritime Antarctic by testing sediments for polychlorinated biphenyls (PCBs) previously identified in soil, flora and fauna of lake catchments. Direct tests of embryo permeability to chemicals are confounded by potential adhesion of chemicals to the embryo surface and limited biomass available. Therefore, in order to assess the potential for lipophilic chemicals to penetrate and passively accumulate in dormant embryos of Antarctic lacustrine zooplankton, we evaluated the effect of anoxia on post-diapause development in the calanoid copepod, Boeckella poppei, and then used chemical anoxia induced by rotenone as a reporter for permeability of these embryos to moderately lipophilic chemicals. The data presented demonstrate that embryos of B. poppei from Antarctic lake sediments will passively accumulate moderately lipophilic chemicals while lying dormant in anoxic sediments. Implications for legacy POPs in sediments of Antarctic maritime lakes are discussed.

Ecotoxicological and biochemical mixture effects of an herbicide and a metal at the marine primary producer diatom Thalassiosira weissflogii and the primary consumer copepod Acartia tonsa

Mixture effects of chemicals and their potential synergistic interactions are of great concern to the public and regulatory authorities worldwide. Intensive agricultural activities are leading to discharges of chemical mixtures to nearby estuarine and marine waters with possible adverse effects on the aquatic communities and for the trophic food web interlinking these communities. Further information about the impacts of these stressors on aquatic organisms is needed. This study addresses ecotoxicological and biochemical effects of single and mixtures of the metal copper and the herbicide Primextra® Gold TZ on the marine diatom Thalassiosira weissflogii and on the estuarine calanoid copepod Acartia tonsa by determining growth rate and survival, respectively, and changes on fatty acid(FA) profiles in both species. Mixture effects on diatom species revealed that copper and Primextra® acted most likely additively with respect to the concentration addition (CA) and independent action (IA) models with model deviation ratios (MDR), 0.752 and 1.063, respectively. For the copepod species, copper and Primextra® were most likely non-interactive with respect to the CA model (MDR = 1.521) but acted most likely synergistically with respect to the IA model (MDR = 2.026). A significant decline in the absolute FA concentration was observed for copepod species after mixture exposure including a considerable decrease of essential FAs that cannot be synthesized de novo by these grazers. We concluded that the mixture effects are more hazardous for primary consumer than for primary producer species in terms of both abundance and biomass quality, suggesting a potential for harmful effects for higher trophic levels and thus a decrease in energy flow through the ecosystem.

Carbon starvation induces lipid degradation via autophagy in the model alga Micrasterias

Autophagy is regarded as crucial intracellular process in plant development but also in intracellular stress response. It is known to be controlled by the energy level of the cell and consequently can be triggered by energy deprivation. In this study carbon starvation evoked in different ways was investigated in the freshwater algae model system Micrasterias denticulata (Streptophyta) which is closely related to higher plants. Cells exposed to the photosynthesis inhibiting herbicide DCMU, to the glycolysis inhibitor 2-Deoxy-d-glucose and to complete darkness over up to 9 weeks for preventing metabolism downstream of glucose supply, were investigated by means of Nile red staining and analyses in CLSM, and TEM after cryo-preparation. Our results show that lipid bodies containing both neutral and polar lipids are evenly distributed inside the chloroplast in control cells. During carbon starvation they are displaced into the cytoplasm and are either degraded via autophagy and/or excreted from the cell. Upon discharge from the chloroplast lipid bodies become engulfed by double membranes probably deriving from the ER, thus forming autophagosomes which later fuse with vacuoles. Coincidently indications for autophagy of other organelles and cytoplasmic portions were found during starvation and particularly in DCMU treated cells the number of starch grains decreased and pyrenoids disintegrated. Additionally our molecular data provide first evidence for the existence of a single ATG8 isoform in Micrasterias. ATG8 is known as main regulator of both bulk and selective autophagy in eucaryotes. Our study indicates that lipid degradation during carbon starvation is achieved via "classical" autophagy in the alga Micrasterias. This process has so far only been very rarely observed in plant cells and seems to allow recruitment of lipids for energy supply on the one hand and elimination of unusable or toxicated lipids on the other hand.

Autophagy-like processes are involved in lipid droplet degradation in Auxenochlorella protothecoides during the heterotrophy-autotrophy transition

Autophagy is a cellular degradation process that recycles cytoplasmic components in eukaryotes. Although intensively studied in yeast, plants, and mammals, autophagy in microalgae is not well understood. Auxenochlorella protothecoides is a green microalga that has the ability to grow either autotrophically when under light or heterotrophically when in media containing glucose. The two growth modes are inter-convertible and transition between them is accompanied by drastic changes in morphology and cellular composition; however, the mechanisms underlying these changes are unknown. In this study, we identified autophagy-related genes and characterized their roles in the degradation of lipid droplets during the heterotrophy-to-autotrophy (HA) transition in A. protothecoides. Most of the proteins constituting the eukaryotic "core machinery" were conserved in A. protothecoides. Two proteins, Atg4 and Atg8, were further investigated. A. protothecoides ATG4 was cloned from a cDNA library and expressed within yeast, and was able to functionally restore the autophagy pathway in atg4Δ yeast during nitrogen starvation. Furthermore, Atg8, which displayed high sequence identity with its yeast homolog, was able to conjugate to phosphatidylethanolamine (PE) in vitro and was recruited to the phagophore assembly site in yeast. We also identified a C-terminal glycine residue, G118, that was the cleavage site for Atg4. Finally, we used confocal and transmission electron microscopy to reveal that autophagic-like vacuoles were detectable in algal cells during the HA transition. Our data suggested that the lipid droplets in heterotrophic cells were engulfed directly by the autophagic-like vacuole instead of via autophagosomes.

Estrogen-receptor independent effects of two ubiquitous environmental estrogens on Melosira varians Agardh, a common component of the aquatic primary production community

Estrogenic compounds have been discovered in many surface water samples in many anthropogenically altered surface waters. Wastewater effluent has been identified as a major pathway of contamination and found to revert much of the metabolic products of these biologically active compounds back to their original form. This presentation explains methodology for determining exposure effects through a newly developed bioassay, examining the physiological response of a diatom to these compounds. Diatoms represent an important aspect of the primary production community. They are a desirable food source over other members of the primary production community through storage of photosynthetically produced sugars in the form of lipids rather than starch. Therefore, many members of higher trophic levels selectively feed on diatoms when present with other members of the primary production community. This study examines the effects of 17beta-estradiol and 4-nonylphenol on the physiological development of the diatom species Melosira varians. Clearly, unicellular protists such as diatoms are not susceptible to these contaminants in a manner directly analogous to that expressed in vertebrates. However, estradiol and nonylphenol are lipophilic making them particularly effective in entering the diatom cell membrane. Melosira varians was selected because it commonly occurs in most freshwater environments and has been the subject of other toxicological studies. An adequate literature base also exists for evaluating results of this experiment. The species grows rapidly and is easy to maintain in culture. Comparing cell density, chl-a, and lipid content in control and exposed cultures allowed interpretation of how the species responded to varying compound concentrations. Results of this study revealed differences in responses to each compound. 17beta-estradiol appears to have no detrimental effect on M. varians, while 4-nonylphenol results in cell mortality with sufficient dosage. Similar results with 17beta-estradiol are reported for other autotrophic organism, but the 4-nonylphenol response is not as uniform in other photosynthetic groups. The use of a phytoplankton species as a test organism complements other investigations involving vertebrate models at or near the apex of the trophic hierarchy by considering effects at the base of the food web.

Toxicant interactions with food algae: a missing link between laboratory and field effects?

Algae fed to invertebrate subjects of chronic toxicity testing are cultured without exposure to test substances. This approach may reduce the ability of bioassays to predict field effects because it assumes that bioconcentration is the only important uptake route, and that an interaction between toxicant and algae does not occur or is not relevant to the effect of the toxicant on test animals. The research presented in this paper focuses on the effects of a bleached kraft mill effluent (BKME) on algae used as food for test animals and the possible consequences of this exposure to bioassay results. The experiment consisted of exposing cultures of a pennate diatom, Navicula, to a range (0-7%) of BKME concentrations for 15 days. Final biomass (measured as chlorophyll a and ash free dry mass) was significantly greater in cultures exposed to 5% and 7% BKME. The carbon-to-nitrogen ratio was significantly higher in diatom cultures exposed to 7% BKME, and total lipid content ranged from 11.7% in the control to 15.8% in the 7% treatment. BKME exposure also increased bacterial content and altered the elemental composition (particularly strontium, barium, iron, and cobalt) of Navicula relative to control cultures. Because changes in food abundance and food quality (e.g., dietary lipids, carbohydrates, proteins) are known to modify toxicity and because contaminant uptake can occur through ingestion, exposing algal food supplies to toxicants would allow chronic bioassays to better simulate field conditions. This approach would be of value in situations where bioassays are intended to predict field effects rather than to compare the toxic potential of effluent samples. Although culturing food algae under exposure to contaminants poses methodological challenges, this approach may serve to enhance the predictive ability of chronic bioassays.

Effects of trichlorobenzene on natural phytoplankton populations

Natural phytoplankton assemblages from an offshore station in Lake Michigan were exposed to individual isomers of trichlorobenzene (TCB) and incubated in situ for a 24 h period. One set of exposures was initiated with a lake assemblage collected at 0330 h from 30 m and the TCB isomers added at 0400 h. The second exposure experiment was initiated with an assemblage from 30 m collected at 1530 h and the TCB isomers added at 1600 h.Comparisons of the chlorophyll a to neutral lipid ratio and the neutral to polar lipid ratios suggest that 1,2,3-TCB is more toxic than 1,2,4-TCB. Furthermore, more effects were observed when exposures were initiated at 0400 h when compared with a parallel experiment initiated at 1600 h. These studies with natural assemblages support culture studies of effect as a function of time of exposure.