Earthworms Produce phytochelatins in Response to Arsenic

Abstract

Phytochelatins are small cysteine-rich non-ribosomal peptides that chelate soft metal and metalloid ions, such as cadmium and arsenic. They are widely produced by plants and microbes; phytochelatin synthase genes are also present in animal species from several different phyla, but there is still little known about whether these genes are functional in animals, and if so, whether they are metal-responsive. We analysed phytochelatin production by direct chemical analysis in Lumbricus rubellus earthworms exposed to arsenic for a 28 day period, and found that arsenic clearly induced phytochelatin production in a dose-dependent manner. It was necessary to measure the phytochelatin metabolite concentrations directly, as there was no upregulation of phytochelatin synthase gene expression after 28 days: phytochelatin synthesis appears not to be transcriptionally regulated in animals. A further untargetted metabolomic analysis also found changes in metabolites associated with the transsulfuration pathway, which channels sulfur flux from methionine for phytochelatin synthesis. There was no evidence of biological transformation of arsenic (e.g. into methylated species) as a result of laboratory arsenic exposure. Finally, we compared wild populations of earthworms sampled from the field, and found that both arsenic-contaminated and cadmium-contaminated mine site worms had elevated phytochelatin concentrations.

Sub-lethal cadmium exposure increases phytochelatin concentrations in the aquatic snail Lymnaea stagnalis

“…Studies on metal pollution which have not analysed PCs may turn out to give an incomplete picture . Indeed, recent studies have shown direct responses of PCs to metal(loid) ions in animal species from additional phyla, including earthworms (Annelida) and sea squirts (Chordata) (Franchi et al, 2014;Liebeke et al, 2013). This, again, highlights the potential significance of PCs in the context of environmental pollution research, as they are found in phyla with members from the terrestrial, freshwater, and marine environments.…”

“…Following centrifugation (5 min, 16,000 g), the supernatants were derivatized with 60 μl of 266 mM N-ethyl maleimide. We then analysed the phytochelatins PC 2 and PC 3 using a targetted LC-MS-MS method, based on the approach of Liebeke et al (2013). Briefly, samples were injected onto an Agilent 1200 HPLC system coupled to a SCIEX 6500 Q-TRAP mass spectrometer (AB SCIEX, Warrington, UK) operated in High Mass negative mode.…”

“…At least some mollusc species contain PCS genes, including gastropod and bivalve species , and PCS gene transcription was affected in response to metal ions in the mussel Bathymodiolus azoricus (Bougerol et al, 2015). However, gene expression is probably not a reliable reporter of actual changes in the functional end products, the PCs (Essig et al, 2016;Liebeke et al, 2013). In the present study we exposed a mollusc species, the freshwater snail Lymnaea stagnalis, to sub-lethal levels of cadmium (Cd), and used direct biochemical detection of PCs to determine the snails' response.…”

Auranofin-induced oxidative stress causes redistribution of the glutathione pool in Taenia crassiceps cysticerci

“…These are: (i) a homologous of ␥-glutamyl transpeptidase, the enzyme responsible for the exogenous degradation of glutathione (Table S1), suggesting that these parasites have the ability to catch and metabolize exogenous glutathione [51]; (ii) the enzyme phytochelatin synthase (Table S2), which is involved in the generation of the glutathione-derived biopolymers named phytochelatins [52]. Although the importance of this enzyme is unknown [53], it has been proposed that could be involved in metal detoxification that can generate ROS [54], as well as in elimination of compounds generated with glutathione S-transferase [55]. In this sense, in preliminary HPLC experiments, we have found the presence of three low molecular weight thiol-containing peptides (Fig.…”

Metallothioneins May Not Be Enough—The Role of Phytochelatins in Invertebrate Metal Detoxification

“…A recent study has now given us a third data point: the earthworm Lumbricus rubellus (phylum Annelida) produced phytochelatins in response to arsenic, both in laboratory exposures ( Figure 1) and in worms sampled from contaminated field sites. 5 Admittedly, this means we still only have data from three phyla, but it does demonstrate that phytochelatin responsiveness to PTEs is not unique to nematodes.…”