Heavy metal detoxification in crustacean epithelial lysosomes: role of anions in the compartmentalization process

Subcellular responses of fish cells to sewage effluents: Cell line-based and whole-animal based approaches

Acute toxicity determination is essential in the ecological risk assessment. Traditionally, acute toxicity testing requires substantial numbers of animals and uses death as an apical end point which requires large number of experimental animals and takes days to obtain the results. Application of fish cell lines can provide a possible alternative to traditional acute toxicity test. However, cell-based assay may show several orders of magnitude less sensitive than the animal-based results. Some changes in cellular organelles could have the sensitivity in responding to pollutants. For this reason, a cell-based fluorescent assay was developed using rabbitfish fin cells as model and fluorescent probes to visualize the subcellular responses. The subcellular responses under sewage effluents exposure were captured by confocal microscopy. These cellular responses were quantified and several subcellular indexes represented the toxicity. The optimized assay was then used to determine the toxicity of sewage effluents displaying toxicity to aquatic animals. Through visualization of cellular responses, we further screened several cellular indexes including lysosomal number and mitochondrial size which had a good linear relationship with sewage effluents content. Besides, these cellular indexes had a good agreement between in vivo and in vitro results, demonstrating the accuracy of cellular parameters in representing the acute toxicity of sewage effluents. The developed cell-based testing assay presented here has the characteristics of a faster and cheaper method, which does not require complex facilities and large amount of testing samples. The developed assay may be further applied in predicting the acute toxicity to sewage effluents.

Transcriptional response of Meloidogyne incognita to non-fumigant nematicides

There is limited research about the impacts of new nematicides, including fluazaindolizine, fluopyram, and fluensulfone, on the plant-parasitic nematode Meloidogyne incognita, despite it being a pervasive agricultural pest. In this study, M. incognita second-stage juveniles were exposed for 24-h to fluensulfone, fluazaindolizine, fluopyram, and oxamyl and total RNA was extracted and sequenced using next-generation sequencing to determine gene expression. The effects of nematicide exposure on cellular detoxification pathways, common differentially expressed (DE) genes, and fatty acid and retinol-binding genes were examined. Fluopyram and oxamyl had the smallest impacts on the M. incognita transcriptome with 48 and 151 genes that were DE, respectively. These compounds also elicited a weak response in the cellular detoxification pathway and fatty acid and retinol-binding (FAR) genes. Fluensulfone and fluazaindolizine produced robust transcriptional responses with 1208 and 2611 DE genes, respectively. These compounds had strong impacts on cellular detoxification, causing differential regulation of transcription factors and genes in the detox pathway. These compounds strongly down-regulated FAR genes between 52-85%. Having a greater understanding of how these compounds function at a molecular level will help to promote proper stewardship, aid with nematicide discovery, and help to stay a step ahead of nematicide resistance.

The transfer of trace metals in the soil-plant-arthropod system

Essential and non-essential trace metals are capable of causing toxicity to organisms above a threshold concentration. Extensive research has assessed the behaviour of trace metals in biological and ecological systems, but has typically focused on single organisms within a trophic level and not on multi-trophic transfer through terrestrial food chains. This reinforces the notion of metal toxicity as a closed system, failing to consider one trophic level as a pollution source to another; therefore, obscuring the full extent of ecosystem effects. Given the relatively few studies on trophic transfer of metals, this review has taken a compartment-based approach, where transfer of metals through trophic pathways is considered as a series of linked compartments (soil-plant-arthropod herbivore-arthropod predator). In particular, we consider the mechanisms by which trace metals are taken up by organisms, the forms and transformations that can occur within the organism and the consequences for trace metal availability to the next trophic level. The review focuses on four of the most prevalent metal cations in soil which are labile in terrestrial food chains: Cd, Cu, Zn and Ni. Current knowledge of the processes and mechanisms by which these metals are transformed and moved within and between trophic levels in the soil-plant-arthropod system are evaluated. We demonstrate that the key factors controlling the transfer of trace metals through the soil-plant-arthropod system are the form and location in which the metal occurs in the lower trophic level and the physiological mechanisms of each organism in regulating uptake, transformation, detoxification and transfer. The magnitude of transfer varies considerably depending on the trace metal concerned, as does its toxicity, and we conclude that biomagnification is not a general property of plant-arthropod and arthropod-arthropod systems. To deliver a more holistic assessment of ecosystem toxicity, integrated studies across ecosystem compartments are needed to identify critical pathways that can result in secondary toxicity across terrestrial food-chains.

Testing the bioaccumulation potential of manufactured nanomaterials in the freshwater amphipod Hyalella azteca

Standardized experimental approaches for the quantification of the bioaccumulation potential of nanomaterials in general and in (benthic) invertebrates in particular are currently lacking. We examined the suitability of the benthic freshwater amphipod Hyalella azteca for the examination of the bioaccumulation potential of nanomaterials. A flow-through test system that allows the generation of bioconcentration and biomagnification factors was applied. The feasibility of the system was confirmed in a 2-lab comparison study. By carrying out bioconcentration and biomagnification studies with gold, titanium dioxide and silver nanoparticles as well as dissolved silver (AgNO₃) we were able to assess the bioaccumulation potential of different types of nanomaterials and their exposure pathways. For this, the animals were examined for their total metal body burden using inductively coupled mass spectroscopy (ICP-MS) and for the presence of nanoparticulate burdens using single-particle ICP-MS. The role of released ions was highlighted as being very important for the bioavailability and bioaccumulation of metals from nanoparticles for both examined uptake paths examined (bioconcentration and biomagnification). In 2018 a tiered testing strategy for engineered nanomaterials was proposed by Handy et al. that may allow a waiver of bioaccumulation fish studies using inter alia invertebrates. Data gained in studies carried out with invertebrates like the developed Hyalella azteca test may be included in this proposed tiered testing strategy.

Unravelling the molecular mechanisms of nickel in woodlice

During the last few years, there has been an alarming increase in the amount of nickel (Ni) being released into the environment, primarily due to its use in the production of stainless steel but also from other sources such as batteries manufacturing and consequent disposal. The established biotic ligand models provide precise estimates for Ni bioavailability, in contrast, studies describing the mechanisms underpinning toxicological effect of Ni are scarce. This study exploits RNA-seq to determine the transcriptomic responses of isopods using Porcellionides pruinosus as an example of a terrestrial metal-resistant woodlouse. Furthermore, the recently proposed model for Ni adverse outcome pathways (Ni-AOP) presents an unprecedented opportunity to fit isopod responses to Ni toxicity and define Porcellionides pruinosus as a metalomic model. Prior to this study, P. pruinosus represented an important environmental sentinel, though lacking genetic/omic data. The reference transcriptome generated here thus represents a major advance and a novel resource. A detailed annotation of the transcripts obtained is presented together with the homology to genes/gene products from Metazoan and Arthropoda phylum, Gene Ontology (GO) classification, clusters of orthologous groups (COG) and assignment to KEGG metabolic pathways. The differential gene expression comparison was determined in response to nickel (Ni) exposure and used to derive the enriched pathways and processes. It revealed a significant impact on ion trafficking and storage, oxidative stress, neurotoxicity, reproduction impairment, genetics and epigenetics. Many of the processes observed support the current Ni-AOP although the data highlights that the current model can be improved by including epigenetic endpoints, which represents key chronic risks under a scenario of Ni toxicity.

Transcriptome Analysis of Hepatopancreas from the Cr (VI)-Stimulated Mantis Shrimp ( Oratosquilla oratoria) by Illumina Paired-End Sequencing: Assembly, Annotation, and Expression Analysis

Cr (VI), the pathogenicity factor, is widely known to cause toxic effects in living organisms. Given the economic importance of the mantis shrimp ( Oratosquilla oratoria), the understanding of impacts by Cr (VI) is considered important. In this study, transcriptome of mantis shrimp was characterized by a comparison between control and Cr (VI)-treated samples using RNA-seq approach. Totally, 88 234 826 bp and 13.24G clean reads were obtained. The total length and number of unigenes were 68 411 206 bp and 100 918, respectively. The maximal and average length of unigenes was 24 906 bp and 678 bp, respectively (N50, 798 bp). 7115 of these unigenes accounted for 7.05% of the total that were annotated in all databases. After annotation of assembled unigenes, 35 619 of them were assigned into 3 functional categories and 56 subcategories using Gene Ontology; 18 580 of them were assigned into 26 functional categories using Clusters of Orthologous Groups of proteins; 16 864 of them were assigned into 5 major categories and 32 subclasses using KEGG. Finally, 1730 genes were differentially expressed (DGEs), 9 up-regulated pathways (protein digestion and absorption, neuroactive ligand-receptor interaction, pancreatic secretion, tyrosine metabolism, amoebiasis, ECM-receptor interaction, riboflavin metabolism, amino sugar and nucleotide sugar metabolism and AGE-RAGE signaling pathway in diabetic complications) were significantly enriched ( q < 0.05), and one down-regulated pathway ( Staphylococcus aureus infection) was significantly enriched ( q < 0.05). Up-regulation of genes in pathways of protein digestion/absorption ( PepT1/SLC15A and ATP1B) and environment information processing ( COL1AS, COL4A; LAMA3_5, LAMB3; FN1 and TN) may imply the potentially positive toxicity resistance mechanisms.

Sulfur vesicles from Thermococcales: A possible role in sulfur detoxifying mechanisms

The euryarchaeon Thermococcus prieurii inhabits deep-sea hydrothermal vents, one of the most extreme environments on Earth, which is reduced and enriched with heavy metals. Transmission electron microscopy and cryo-electron microscopy imaging of T. prieurii revealed the production of a plethora of diverse membrane vesicles (MVs) (from 50 nm to 400 nm), as is the case for other Thermococcales. T. prieurii also produces particularly long nanopods/nanotubes, some of them containing more than 35 vesicles encased in a S-layer coat. Notably, cryo-electron microscopy of T. prieurii cells revealed the presence of numerous intracellular dark vesicles that bud from the host cells via interaction with the cytoplasmic membrane. These dark vesicles are exclusively found in conjunction with T. prieurii cells and never observed in the purified membrane vesicles preparations. Energy-Dispersive-X-Ray analyses revealed that these dark vesicles are filled with sulfur. Furthermore, the presence of these sulfur vesicles (SVs) is exclusively observed when elemental sulfur was added into the growth medium. In this report, we suggest that these atypical vesicles sequester the excess sulfur not used for growth, thus preventing the accumulation of toxic levels of sulfur in the host's cytoplasm. These SVs transport elemental sulfur out of the cell where they are rapidly degraded. Intriguingly, closely related archaeal species, Thermococcus nautili and Thermococcus kodakaraensis, show some differences about the production of sulfur vesicles. Whereas T. kodakaraensis produces less sulfur vesicles than T. prieurii, T. nautili does not produce such sulfur vesicles, suggesting that Thermococcales species exhibit significant differences in their sulfur metabolic pathways.

Metal/metalloid accumulation/remobilization during aquatic litter decomposition in freshwater: a review

The focus of this article is to combine two main areas of research activities in freshwater ecosystems: the effect of inorganic pollutants on freshwater ecosystems and litter decomposition as a fundamental ecological process in streams. The decomposition of plant litter in aquatic systems as a main energy source in running water ecosystems proceeds in three distinct temporal stages of leaching, conditioning and fragmentation. During these stages metals and metalloids may be fixed by litter, its decay products and the associated organisms. The global-scale problem of contaminated freshwater ecosystems by metals and metalloids has led to many investigations on the acute and chronic toxicity of these elements to plants and animals as well as the impact on animal activity under laboratory conditions. Where sorption properties and accumulation/remobilization potential of metals in sediments and attached microorganisms are quite well understood, the combination of both research areas concerning the impact of higher trophic levels on the modification of sediment sorption conditions and the influence of metal/metalloid pollution on decomposition of plant litter mediated by decomposer community, as well as the effect of high metal load during litter decay on organism health under field conditions, has still to be elucidated. So far it was found that microbes and invertebrate shredder (species of the genera Gammarus and Asellus) have a significant influence on metal fixation on litter. Not many studies focus on the impact of other functional groups affecting litter decay (e.g. grazer and collectors) or other main processes in freshwater ecosystems like bioturbation (e.g. Tubifex, Chironomus) on metal fixation/release.

Enhanced metal and metalloid concentrations in the gut system comparing to remaining tissues of Gammarus pulex L

Invertebrate shredders such as Gammarus pulex are key species in contaminated stream ecosystems. Although a number of previous studies examining differences in metal accumulation between the gut system and remaining tissues of invertebrates exist, few focus on wide range of metals and metalloids that are relevant to contaminated systems. This study compared accumulation of the commonest (at study site) 15 metals and metalloids between the gut system including feces and remaining tissues of G. pulex. All metals and metalloids measured were significantly higher (p<0.001, except Cu p<0.005) in the gut system including feces than remaining tissues of G. pulex. Metals and metalloids in body tissues without the gut system including feces were significantly lower (Al, Cr, Fe and Mn (p<0.005), Sr and U (p<0.01), Co (p<0.05)) in content for a number of elements when compared to washed, whole G. pulex specimens. As well, all elements measured were significantly higher (all elements (p<0.005) except Cu and Co (p<0.05)) in gut system including feces than washed, whole G. pulex specimens. These results indicate that in G. pulex the uptake of all 15 metals and metalloids examined across the gut epithelium is minimalized or that sequestration of these elements in gut epithelial cells may occur.

Oxalate efflux transporter from the brown rot fungus Fomitopsis palustris

An oxalate-fermenting brown rot fungus, Fomitopsis palustris, secretes large amounts of oxalic acid during wood decay. Secretion of oxalic acid is indispensable for the degradation of wood cell walls, but almost nothing is known about the transport mechanism by which oxalic acid is secreted from F. palustris hyphal cells. We characterized the mechanism for oxalate transport using membrane vesicles of F. palustris. Oxalate transport in F. palustris was ATP dependent and was strongly inhibited by several inhibitors, such as valinomycin and NH(4)(+), suggesting the presence of a secondary oxalate transporter in this fungus. We then isolated a cDNA, FpOAR (Fomitopsis palustris oxalic acid resistance), from F. palustris by functional screening of yeast transformants with cDNAs grown on oxalic acid-containing plates. FpOAR is predicted to be a membrane protein that possesses six transmembrane domains but shows no similarity with known oxalate transporters. The yeast transformant possessing FpOAR (FpOAR-transformant) acquired resistance to oxalic acid and contained less oxalate than the control transformant. Biochemical analyses using membrane vesicles of the FpOAR-transformant showed that the oxalate transport property of FpOAR was consistent with that observed in membrane vesicles of F. palustris. The quantity of FpOAR transcripts was correlated with increasing oxalic acid accumulation in the culture medium and was induced when exogenous oxalate was added to the medium. These results strongly suggest that FpOAR plays an important role in wood decay by acting as a secondary transporter responsible for secretion of oxalate by F. palustris.

Dual control of cytosolic metals by lysosomal transporters in lobster hepatopancreas

This study describes the membrane transport mechanisms used by lobster (Homarus americanus) hepatopancreatic epithelial lysosomes to accumulate and sequester heavy metals from the cytosol, and thereby aid in the regulation of these ions entering the animal from dietary constituents. The present investigation extends previous work describing lysosomal metal uptake by cation exchange with protons and suggests that a second, parallel, lysosomal transport process involving metal—thiol conjugates may work in conjunction with the cation antiporter to control cytoplasmic metal concentrations. Transport of 65Zn2+ by lysosomal membrane vesicles (LMV) incubated in 1 mmol l−1 glutathione (GSH) was not significantly different from metal transport in the absence of the tripeptide. However, preloading LMV with 1 mmol l−1 α-ketoglutarate (AKG), and then incubating in a medium containing 1 mmol l−1 GSH, more than doubled metal uptake, compared with vesicles equilibrated with chloride or possessing an outwardly directed chloride gradient. Kinetic analysis of lysosomal 65Zn2+ influx as a function of zinc concentration, in vesicles containing 1 mmol l−1 AKG and incubated in 1 mmol l−1 GSH, revealed the presence of a sigmoidal, low affinity, high capacity carrier process transporting the metal into the organelle. These data indicated the possible presence of an organic anion exchanger in lobster lysosomal membranes. Western blot analysis of LMV with a rabbit anti-rat OAT1 antibody showed the presence of an orthologous OAT1-like protein (approximate molecular mass of 80 kDa) signal from these membranes. These results, and those published previously, suggest the occurrence of two metal transporters on hepatopancreatic membranes, a high affinity, low capacity cation antiporter and a low affinity, high capacity organic anion exchanger. Together these two systems have the potential to regulate cytoplasmic metals over a wide concentration range.

A comparative study on the influence of manganese on the bactericidal response of marine invertebrates

Manganese, Mn, is a naturally abundant metal in marine sediments. During hypoxic conditions the metal converts into a bioavailable state and can reach levels that have been shown immunotoxic to the crustacean Nephrops norvegicus. For this species it has previously been shown that exposure to 15 mg L(-1) of Mn decreased the number of circulating haemocytes while it for the echinoderm Asterias rubens increased the number of coelomocytes. Here, we compared if five days of exposure to the same concentration of Mn affects the bactericidal capacity of these two species and the mollusc Mytilus edulis when inoculated with the bacterium Vibrio parahaemolyticus. Viable counts of the bacteria were investigated at a time-course post-injection in the blood and the digestive glands of Mn-exposed and un-exposed (controls) animals. Accumulation of Mn was also analyzed in these tissues. When exposed to Mn the haemocyte numbers were significantly reduced in M. edulis and it was shown that the bactericidal capacity was impaired in the mussels as well as in N. norvegicus. This was most obvious in the digestive glands. These two species also showed the highest accumulation of the metal. In A. rubens the bactericidal capacity was not affected and the metal concentration was similar to the exposure concentration. After a recovery period of three days the concentration of Mn was significantly reduced in all three species. However, in M. edulis and N. norvegicus it was still double that of A. rubens which could explain the remaining bactericidal suppression observed in N. norvegicus. This study pointed out that exposure to such Mn-levels that are realistic to find in nature could have effects on the whole organism level, in terms of susceptibility to infections. The effect seemed associated to the accumulated concentration of Mn which differed on species level.