Impacts of nanoparticles to microbes and invertebrates: from community responses to cellular targets

The incredible development in nanotechnology since the last decade has brought the “nanoworld” to our regular life. However, the extensive global growth in commercial production and usage of nanomaterial-based products raised the question whether nanomaterials when released to the environment can constitute a potential risk to biota and ecosystem processes. Being large reservoirs, natural waters are likely to be the ultimate sink of nanomaterials. In forested streams, microbes, predominantly fungi, decompose plant litter from riparian vegetation and transfer carbon and energy via invertebrate shredders to higher trophic levels. Freshwater decomposers are sensitive to changes in water quality with implications to ecosystem functioning. Considering the recent development of nanotechnology, assessing the potential toxicity of nanomaterials against freshwater decomposers and examining their ecological and physiological responses to nanoparticle exposure will contribute to a safer use of nanomaterials. In this study, by using a microcosm approach, we found that nanocopper oxide (nanoCuO), nanosilver, and their ionic precursors severely affected leaf litter decomposition by stream-dwelling microbes, as indicated by a decrease in microbial biomass, fungal sporulation and species richness. Moreover, the analysis of fungal and bacterial communities, based on DNA fingerprints from denaturing gradient gel electrophoresis and fungal sporulating species, revealed shifts in species composition and changes towards a better adapted community under the stress induced by nano and ionic metals. Moreover, the negative effects of metal nanoparticles were less pronounced than those of their ionic forms. Nanoparticle size (12, 50 and 80 nm) and the presence of humic acid (HA) influenced the toxicity of nanoCuO against stream-dwelling microbial decomposers. The toxicity of nanoCuO increased in a dose-dependent manner and with the decrease in nanoparticle size. Bacteria were more sensitive than fungi to nanoCuO, because EC50 values for biomass of bacteria were much lower than those of fungi. Fungal reproduction was more sensitive to nanoCuO than leaf decomposition or microbial biomass. HA alone also had negative effects on microbial diversity and activity, but the presence of HA alleviated the negative effects of smaller size nanoCuO (12 or 50 nm). Alterations in leaf surface morphology further supported the impacts of nanoparticles and HA on microbial activity on decomposing leaves, as shown by scanning electron microscopy. We also showed that nanoCuO had lethal and sublethal effects on Allogamus ligonifer, a common invertebrate shredder in Southwest European streams that prefers high quality stream water. The feeding behaviour and growth of the invertebrate were affected in a dose-dependent manner. Effects were due to both nanoCuO and ionic copper leached from nanoCuO that adsorbed or accumulated in the shredder body. The feeding behaviour of the invertebrate shredder was more inhibited as nanoparticle size decreased. The toxicity of smaller size nanoCuO to the shredder was alleviated by the presence of HA. A postexposure feeding experiment showed a very low recovery of the invertebrate feeding behaviour after stress removal. The exposure of aquatic fungal populations to nanoCuO led to a decrease in biomass production, alterations in cell-wall morphology, increased biosorption of nanoCuO and induction of extracellular laccase activity in a time and dose-dependent manner. Fungal populations from metal-polluted streams were more resistant/tolerant to the stress induced by nanoCuO than those from non-polluted streams. Differences in laccase activity among fungi appeared to be related to the presence of laccase-like genes in the copper-binding domain. Exposure to nanoCuO or ionic copper led to lower intracellular accumulation of reactive oxygen species (ROS), plasma membrane disruption, and DNA-strand breaks in fungal populations isolated from metal-polluted streams than in those from non-polluted streams. The activities of glutathione reductase and superoxide dismutase were higher in fungi from metal-polluted than from non-polluted streams, but the opposite was found for glutathione peroxidase activity. Results suggested that fungi from metal-polluted streams have higher capacity to deal with the oxidative stress induced by nanoCuO, probably due to their ability to maintain a high ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG). In contrast to metal nanoparticles, polyhydroxy fullerene (PHF) nanoparticles stimulated the growth of the yeast Saccharomyces cerevisiae, which was used as model of eukaryotic organism. Moreover, the oxidative stress induced by cadmium ions to yeast cells was mitigated by the presence of PHF. A maximum growth recovery was obtained after 26h of exposure to 500 ppm PHF at pH 6.8. Results suggested that PHF nanoparticles have antioxidant and free-radical scavenging properties.

Name thesis:degree_name

Tese de doutoramento in Sciences Specialization in Biology

Year dc:date.issued

2013

Author dc:creator

• Pradhan, Arunava

Advisors dc:contributor.advisor

• Cássio, Fernanda
• Pascoal, Cláudia
• Sahadevan, Seena

Statement dc:rights

• openAccess

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/1822/27372

OAI record oai:identifier

http://repositorium.sdum.uminho.pt/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Arepositorium.uminho.pt%3A1822%2F27372