Abstract of PhD Thesis

Evaluating the suitability of the nematode Steinernema feltiae as an environmental indicator

Eileen Kelly, Institute of Technology Carlow, 2015

Heavy metal contamination can be a serious environmental problem affecting terrestrial ecosystems and can accumulate in food webs. In Ireland, and elsewhere, disused mines potentially contribute to this problem, as the environmental damage continues long after the mines have been closed. Nematodes occupy key positions as primary and intermediate consumers in soil ecosystems and, as such, are useful bio-indicator organisms for environmental monitoring. Entomopathogenic nematodes (EPN; Steinernematidae and Heterorhabditidae) are soil-inhabiting, obligate bacteria-feeding nematodes, whose dauer juveniles serve as an infective stage that seeks and invades suitable insect hosts in the soil. These nematodes are naturally occurring in Ireland. The chosen species for this study is the well-characterised EPN Steinernema feltiae (Filipjev). Lead, cadmium and zinc, which are associated with mining in Ireland (e.g. Silvermines), were chosen for this study, the aim of which was to explore the potential of S. feltiae as a bio-indicator organism of terrestrial heavy metal pollution using laboratory bioassays. These tests measured toxicity lethal (nematode mortality) and sub-lethal (nematode development, infectivity and lifespan) endpoints. The performance of the data generated from the bioassays was assessed using Receiver Operating Characteristic curve (ROC) analysis. The most suitable bioassays to indicate heavy metal contamination in soil using S. feltiae as a sentinel organism were selected. Chemical analysis of the soil alone is sufficient to assess environmental impact, as it does not reflect the effects the pollution has on soil biota. Therefore, the use of nematode bioassays, using toxicity endpoints, is a useful complementary and informative approach when monitoring heavy metal contamination. Cadmium was the heavy metal most detrimental to S. feltiae behaviour. ROC curves indicated that bioassays used to test (a) nematode movement towards the host and (b) nematode fecundity in the presence of heavy metals, proved to be suitable for predicting heavy metal contamination in soil. We propose the use of ROC analysis to verify the efficacy of such bioassays in order to assess toxicity in soil. Previous studies have found that copper affects the mortality and pathogenicity of S. feltiae. Therefore, this nematode could also be used as an environmental indicator for environmental fungicide pollution with copper. The findings of this project can directly impact national environmental policy in adopting nematode-based biomonitoring systems for heavy metal terrestrial pollution using S. feltiae. Currently, three papers are being prepared for submission under international peer review.