Response of Soil Microorganisms to As-Produced and Functionalized Single-Wall Carbon Nanotubes (SWNTs)
The use of single-wall carbon nanotubes (SWNTs) in manufacturing and biomedical applications is increasing at a rapid rate; however data on the effects of a potential environmental release of the materials remain sparse. In this study, soils with either low or high organic matter contents as well as pure cultures of E. coli are challenged with either raw As-Produced SWNTs (AP-SWNTs) or SWNTs functionalized with either polyethyleneglycol (PEG-SWNTs) or m-polyaminobenzene sulfonic acid (PABS-SWNTs). To mimic chronic exposure, the soil systems were challenged weekly for six weeks; microbial activities and community structures for both the prokaryote and eukaryote community were evaluated. Results show that repeated applications of AP-SWNTs can affect microbial community structures and induce minor changes in soil metabolic activity in the low organic matter systems. Toxicity of the three types of SWNTs was also assessed in liquid cultures using a bioluminescent E. coli-O157:H7 strain. Although decreases in light were detected in all treated samples, low light recovery following glucose addition in AP-SWNTs treatment and light absorption property of SWNTs particles suggest that AP-SWNTs suppressed metabolic activity of the E. coli, while the two functionalized SWNTs are less toxic. The metals released from the raw forms of SWNTs would not play a role in the effects seen in soil or the pure culture. We suggest that sorption to soil organic matter plays a controlling role in the soil microbiological responses to these nanomaterials.
Available from: Andrea Clavijo
- "Previous studies utilizing DGGE to assess the impact of CNM in a soil with a higher organic and clay content found minimal change in the microbial community structure with C 60 addition (Tong et al., 2007). Tong et al. later reported that, while certain types of SWCNT significantly altered the community composition in a soil with low clay and low organic matter content (similar to the current study), these same nanomaterials had little effect when applied to a soil with higher clay and organic matter contents (Tong et al., 2012).Tong et al.proposed that soil organic matter and clay are able to mitigate CNM toxicity through strong sorption and aggregation dynamics, however the mechanisms are poorly understood. Interactions with soil dissolved organic matter have been previously studied as important factors in the response of soil to CNM exposure.Espinasse et al. (2007)reported that inclusion of tannic acid in aqueous C 60 suspensions decreased aggregation and enhanced mobility of fullerenes in a porous media (Espinasse et al., 2007). "
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ABSTRACT: Recent studies indicate that while unfunctionalized carbon nanomaterials (CNMs) exhibit very low decomposition rates in soils, even minor surface functionalization (e.g., as a result of photochemical weathering) may accelerate microbial decay. We present results from a C60 fullerene-soil incubation study designed to investigate the potential links between photochemical and microbial degradation of photo-irradiated C60. Irradiating aqueous 13C-labeled C60 with solar-wavelength light resulted in a complex mixture of intermediate products with decreased aromaticity. Although addition of irradiated C60 to soil microcosms had little effect on net soil respiration, excess 13C in the respired CO2 demonstrates that photo-irradiating C60 enhanced its degradation in soil, with ∼0.78% of 60 day photo-irradiated C60 mineralized. Community analysis by DGGE found that soil microbial community structure was altered and depended on the photo-treatment duration. These findings demonstrate how abiotic and biotic transformation processes can couple to influence degradation of CNMs in the natural environment.
Available from: Wenjie Ren
- "Compared with pure cultures and wastewater systems, the soil environment is much more complex and uncontrolled. When graphene enters the soil, it may interact with organic matter or clay minerals present in the soil , stabilizing graphene and making it less bioavailable, which would mitigate the effect of graphene on microbial communities. On the contrary, dissolved organic matter (DOM) might promote the mobility and bioavailability of graphene by acting as natural surfactants . "
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ABSTRACT: The increased application of graphene raises concerns about its environmental impact, but little information is available on the effect of graphene on the soil microbial community. This study evaluated the impact of graphene on the structure, abundance and function of the soil bacterial community based on quantitative real-time polymerase chain reaction (qPCR), pyrosequencing and soil enzyme activities. The results show that the enzyme activities of dehydrogenase and fluorescein diacetate (FDA) esterase and the biomass of the bacterial populations were transiently promoted by the presence of graphene after 4 days of exposure, but these parameters recovered completely after 21 days. Pyrosequencing analysis suggested a significant shift in some bacterial populations after 4 days, and the shift became weaker or disappeared as the exposure time increased to 60 days. During the entire exposure process, the majority of bacterial phylotypes remained unaffected. Some bacterial populations involved in nitrogen biogeochemical cycles and the degradation of organic compounds can be affected by the presence of graphene.
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Available from: Qiao Ma
- "Great attention has been paid to the CNTs' ecological effects on microbe since those microorganisms play key roles in the global biogeochemical cycling of nutrients, biomass decomposition, and waste treatment systems (Kang et al. 2007; Brar et al. 2010). Previous researches have confirmed the adverse impacts of CNTs on both the pure culture bacteria (Kang et al. 2007; Pasquini et al. 2013) and the microbial communities in soil and activated sludge (Goyal et al. 2010; Tong et al. 2012). The antibacterial activity of CNTs enables them to be used in regenerative purification devices to remove viral and bacterial pathogen during waste disposal and purification process (Brady-Estévez et al. 2008). "
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ABSTRACT: To enrich the understanding on interactions between carbon nanotubes (CNTs) and microbes, the responses of a biphenyl-degrading bacterium to single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) and carboxyl single-walled carbon nanotubes (SWCNT-COOHs) were investigated. Electron microscopy, viability test, cellular membrane integrity, and oxidative stress analyses indicated that CNT toxicity was mainly caused by physical piercing. Apart from antibacterial activities, the experimental results showed that CNTs enhanced cell growth and biphenyl degradation at certain concentrations (1.0-1.5 mg/L). The CNTs aggregated and adsorbed cells and biphenyl to form a CNTs-cells-biphenyl coexisting system, thus it created a suitable microenvironment for cell attachment and proliferation where the cells could utilize biphenyl easier for their growth. To the best of our knowledge, this is the first report about CNTs' impact on biodegradation efficacy and growth of aromatic-degrading bacterium.
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