Behaviors of pollutant-degrading microbes and their biodegradation activities to toxicity of metal/ metal oxide nanoparticles.

Abstract

The use of engineered metal nanoparticles (NPs) has raised concerns about their ecotoxic effects. In this study, we evaluated the impact of aluminum (nAl), iron (nFe), nickel (nNi), and zinc (nZn) on dibenzofuran (DF)-degrading bacteria Agrobacterium sp. PH-08. The NPs estimated in this study exists in metal/ metal oxide form: zero valent cores and oxide shells. The size of particles observed in TEM image were under 100nm (nFe (36.3nm) was the smallest while the biggest one was nZn (82.3 nm)). Bacterial cells treated with NPs (0 ~ 1 g l-1) were evaluated for cytotoxicity, genotoxicity, growth and biodegradation activities at biochemical and molecular levels. The aggregated clusters containing bacteria and NPs were observed. In an aqueous system, the cells treated with nAl, nZn and nNi at 0.5 g l-1 showed higher toxicity (36 ~ 78%) than cells treated with nFe. In the presence of nAl, nZn and nNi, the cells showed increased levels of reactive oxygen species, DNA damage and cell death. Furthermore, the NPs significantly inhibited (63~95%) the DF biodegradation and catechol 2,3-dioxygenase activities and its gene (c23o) expression. The NPs penetration into strain PH-08 could be seen only in nZn treatment while the other cases, like nFe, nAl as well as nNi, NPs distributed surround bacterial membrane. The majority of bacterial exoduses can be assumed as a factor in diminishing the toxicity of NPs.