Engineering of a silica encapsulation platform for hydrocarbon degradation using Pseudomonas sp. NCIB 9816-4.
Industrial application of encapsulated bacteria for biodegradation of hydrocarbons in water requires mechanically stable materials. A silica gel encapsulation method was optimized for Pseudomonas sp. NCIB 9816-4, a bacterium that degrades more than 100 aromatic hydrocarbons. The design process focused on three aspects: (i) mechanical property enhancement; (ii) gel cytocompatibility; and (iii) reduction of the diffusion barrier in the gel. Mechanical testing indicated that the compressive strength at failure (σf ) and elastic modulus (E) changed linearly with the amount of silicon alkoxide used in the gel composition. Measurement of naphthalene biodegradation by encapsulated cells indicated that the gel maintained cytocompatibility at lower levels of alkoxide. However, significant loss in activity was observed due to methanol formation during hydrolysis at high alkoxide concentrations, as measured by FTIR spectroscopy. The silica gel with the highest amount of alkoxide (without toxicity from methanol) had a biodegradation rate of 285 ± 42 nmol/L-s, σf  = 652 ± 88 kPa, and E = 15.8 ± 2.0 MPa. Biodegradation was sustained for 1 month before it dropped below 20% of the initial rate. In order to improve the diffusion through the gel, polyvinyl alcohol (PVA) was used as a porogen and resulted in a 48 ± 19% enhancement in biodegradation, but it impacted the mechanical properties negatively. This is the first report studying how the silica composition affects biodegradation of naphthalene by Pseudomonas sp. NCIB 9816-4 and establishes a foundation for future studies of aromatic hydrocarbon biodegradation for industrial application.
Department of Mechanical Engineering, University of Minnesota, 111 Church St SE, Minneapolis, Minnesota, 55455.
Jonathan K
JK
Sakkos
Department of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota.
Daniel P
DP
Kieffer
Department of Mechanical Engineering, University of Minnesota, 111 Church St SE, Minneapolis, Minnesota, 55455.|BioTechnology Institute, University of Minnesota, St. Paul, Minnesota.
Baris R
BR
Mutlu
BioTechnology Institute, University of Minnesota, St. Paul, Minnesota.|Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota.
Lawrence P
LP
Wackett
Department of Mechanical Engineering, University of Minnesota, 111 Church St SE, Minneapolis, Minnesota, 55455. aaksan@umn.edu.|BioTechnology Institute, University of Minnesota, St. Paul, Minnesota. aaksan@umn.edu.
Alptekin
A
Aksan
D001711:Biotransformation; D002214:Capsules; D018914:Cells, Immobilized / Q000378:metabolism*; D006841:Hydrocarbons, Aromatic / Q000378:metabolism*; D000432:Methanol / Q000378:metabolism; D011549:Pseudomonas / Q000378:metabolism*; D058428:Silica Gel; D017550:Spectroscopy, Fourier Transform Infrared
D002214:Capsules; D006841:Hydrocarbons, Aromatic; D058428:Silica Gel; D000432:Methanol
Pseudomonas sp. NCIB 9816-4; aromatic hydrocarbons; biodegradation; bioencapsulation; mechanical properties; silica gel