Potential Impacts of Nanoparticles on Bacterial Systems

• Author / Creator

  Sun, Xiaohui

• With the widespread use of nanoparticles (NPs) in commercial products, it is inevitable that NPs will be released into and accumulated in domestic and industrial waste streams (such as wastewater treatment systems), which might have unknown effects. To determine the effects of Ag NPs on the complex microbial communities present in activated sludge, experiments were performed to determine the effects of 1 mg/L Ag NPs on microbial communities in activated sludge. Activated sludge samples with and without gravity settling were compared to evaluate the impact of activated sludge flocs structure on the response of microbial communities to Ag NPs. The effects of Ag NPs on the entire microbial community in activated sludge were analyzed using 16S rRNA gene based polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). The results suggest that certain microbial species in the intact activated sludge were highly sensitive to Ag NPs treatment, although no reduction in cell culturability was detected through heterotrophic plate counts (HPCs) during the 24 hours Ag NPs treatment. Conversely, one log unit reduction in the HPCs with no microbial community structure changes was observed for unsettled activated sludge flocs (intact activated sludge treated by 3 hours gravity-settling) after 24 hours Ag NPs treatment. These results strongly suggest that Ag NPs can impact the activated sludge microbial community and cell culturability depending on the physical structure of the activated sludge flocs, the spatial distribution of microorganisms in activated sludge flocs, and the community structures in the activated sludge.
  In comparison to metal NPs, cellulose nanocrystals (CNC) is a type of rod-shaped biodegradable NPs. Depletion induced flocculation and phase separation of Pseudomonas aeruginosa PAO1 bacteria due to the presence of CNC particles were observed by using confocal laser scanning microscopy and turbidity measurements. CNC with length of 90 nm, diameter of 8 nm and zeta potential of –51.5 mV (in H2O at neutral pH) was used to investigate the depletion effect of CNC in bacterial systems. Bacterial flocculation was observed at the CNC concentration of less than 0.1% due to the depletion effect. These results indicate that rod-shaped nanosized CNC are effective for the depletion flocculation of colloidal size bacteria and that phase separation of bacteria can occur at very low concentrations of CNC particles. In order to verify the impact of extracellular polymeric substance (EPS) on bacterial aggregation and adhesion in the presence of CNC, deposition on silica surfaces of two Pseudomonas fluorescens strains (CHA0 and CHA19-WS) having different EPS producing capacities, was studied in the absence and presence of CNC. The results demonstrate that bacterial initial adhesion to solid surfaces can be significantly hindered by CNC and this hinderance is related to the mount of EPS. In the presence of CNC, bacteria with more EPS aggregated more significantly compared to bacteria with less EPS, and that bacterial deposition in this condition decreased to a greater extent. The effects of pH and IS on the aggregation and deposition of E. coli K12 on silica surfaces were investigated in the absence and presence of CNC. The results indicate that at pH ranging from 5.2 to 7.2 and IS ranging from 10 mM to 50 mM conditions, depletion attraction is the dominant mechanism for CNC induced bacterial aggregation.

• Subjects / Keywords

  • Bacterial Aggregation
  • Bacterial Adhesion
  • Nanoparticles
  • Activated Sludge
  • Antimicrobial Effects
  • Wastewater Treatment

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3VM43805

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.