Biodegradation by cells encapsulated in silica gel is an economical and environmentally friendly method for the removal of toxic chemicals from the environment. In this work, recombinant E. coli expressing atrazine chlorohydrolase (AtzA) were encapsulated in organically modified silica (ORMOSIL) gels composed of TEOS, silica nanoparticles (SNPs), and either phenyltriethoxysilane (PTES) or methyltriethoxysilane (MTES). ORMOSIL gels adsorbed much higher amounts of atrazine than the hydrophilic TEOS gels. The highest amount of atrazine adsorbed by ORMOSIL gels was 48.91 × 10 −3 μmol/ml gel, compared to 8.71 × 10 −3 μmol/ml gel by the hydrophilic TEOS gels. Atrazine biodegradation rates were also higher in ORMOSIL gels than the TEOS gels, mainly due to co-localization of the hydrophobic substrate at high concentrations in close proximity of the encapsulated bacteria. A direct correlation between atrazine adsorption and biodegradation was observed unless biodegradation decreased due to severe phase separation. The optimized PTES and MTES gels had atrazine biodegradation rates of 0.041±0.003 and 0.047±0.004 μmol/ml gel, respectively. These rates were approximately 80% higher than that measured in the TEOS gel. This study showed for the first time that optimized hydrophobic gel material design can be used to enhance both removal and biodegradation of hydrophobic chemicals.
Bibliographical noteFunding Information:
This research was supported by a grant from Syngenta Crop Protection , a seed grant from the University of Minnesota BioTechnology Institute , and Vaadia-BARD Postdoctoral Fellowship award no. FI-516-2014 from BARD, the United States-Israel Binational Agricultural Research and Development Fund. Parts of this work were carried out in the Characterization Facility at the University of Minnesota, which receives partial support from NSF though the MRSEC program. Confocal microscopy was done with the help of the University Imaging Centers at the University of Minnesota. NMR work was carried out in the MNMR center at the University of Minnesota, which receives funding from Office of the Vice President for Research, the Medical School, the College of Biological Science, NIH, NSF, and the Minnesota Medical Foundation.
© 2017 Elsevier Inc.
- Encapsulated bacteria
- Hydrophobic silica gel