PERTURBATION OF FOREST SOIL MICROBIAL COMMUNITY BY METAL NANOPARTICLES

Nanotechnology is a growing field with a major role in product and process innovations. This is an opportunity to develop new products, but it also harbors risks for the environment and health. Although it is a common knowledge that some nanoparticles (NPs) have antibacterial activity, there is little information on the influence of NPs on soil microbial community (Hänsch and Emmerling, 2010). The harmful properties of silver ions to bacteria, for example, are well investigated. Silver ions may inhibit bacterial respiratory activity and may negatively interact with the bacterial cell wall enzymes. Furthermore, Ag ions may inhibit DNA replication. Perturbations of soil microbial consortia can have significant consequences for ecosystems and soil microbial consortia are influenced by and also affect plant growth (Davidson and Janssens, 2006). The aim of this work was to assess the impact of Ag, CeO2, Fe3O4, SnO2 NPs on the soil microbial community, to evaluate if NPs can affect the soil quality. 500 mg of NPs / kg of soil were mixed to an A1 horizon of Epileptic Cambisols (sandy clay loam texture; subacid pH) deriving from a forest environment and incubated at constant temperature and controlled moisture (e.g. 25°C and 60% WHC). Aliquots of soil samples were analysed after 30, 60 and 90 days of incubation with NPs to evaluate the following parameters: viable bacterial and moulds/yeasts counts , total soil microbial biomass, estimation of soil respiration, DNA extraction and PCR-DGGE. Preliminary results of the biological assays shows an increment of the basal respiration and a decrease in the amount of carbon soil microbial biomass. The relation between these parameters determine a higher metabolic quotient (qCO2) compared to the control test, that identifies a stressful situation, most evident in the thesis with Ag-NPs. Microbial plate counts evidenced no significant differences among treated and control soil except for a 2 log decrease of viable bacterial count in the Ag-treated soil after 60 days (Ag-60). Moreover, the quantification of soil DNA extractions showed a gradual decrease of DNA concentration in Ag-treated soil during incubation. PCR-DGGE was performed to evaluate NPs impact on microbial soil community. DGGE profile of control soil was mainly conserved in CeO2, Fe3O4 and SnO2 treated samples. On the contrary, Ag-treated soil evidenced a clear different profile already after the first 30 days (Ag-30). Moreover, the profile changed again in Ag-60 and remain stable in Ag-90. It is interesting to note that some bands showed an increased intensity as the incubation with Ag NPs proceeded. This preliminary results show an important influence of the Ag NPs on soil microbial community, decreasing richness and diversity. Bands sequencing are in progress to identify the microbial populations that are positively/negatively affected by NPs treatment.