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Molecules 2018, 23(2), 503; https://doi.org/10.3390/molecules23020503

Bacillus Cellulase Molecular Cloning, Expression, and Surface Display on the Outer Membrane of Escherichia coli

1,2
and
3,*
1
Laboratory of Renewable Resources Engineering, Purdue University, West Lafayette, IN 47907, USA
2
Department of Agricultural and Biological Engineering, Purdue University, West Lafayette, IN 47907, USA
3
Fermentation Science Program, School of Agribusiness and Agriscience, College of Basic and Applied Sciences, Middle Tennessee State University, Murfreesboro, TN 37132, USA
*
Author to whom correspondence should be addressed.
Received: 17 January 2018 / Revised: 21 February 2018 / Accepted: 23 February 2018 / Published: 24 February 2018
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Abstract

One of the main challenges of using recombinant enzymes is that they are derived from genetically-modified microorganisms commonly located in the intracellular region. The use of these recombinant enzymes for commercial purposes requires the additional processes of cell disruption and purification, which may result in enzyme loss, denaturation, and increased total production cost. In this study, the cellulase gene of Bacillus licheniformis ATCC 14580 was cloned, over-expressed, and surface displayed in recombinant Escherichia coli using an ice-nucleation protein (INP). INP, an outer membrane-bound protein from Pseudomonas syringae, was utilized as an anchor linker, which was cloned with a foreign cellulase gene into the pET21a vector to develop a surface display system on the outer membrane of E. coli. The resulting strain successfully revealed cellulase on the host cell surface. The over-expressed INP-cellulase fusion protein was confirmed via staining assay for determining the extracellular cellulase and Western blotting method for the molecular weight (MW) of cellulase, which was estimated to be around 61.7 kDa. Cell fractionation and localization tests demonstrated that the INP-cellulase fusion protein was mostly present in the supernatant (47.5%) and outer membrane (19.4%), while the wild-type strain intracellularly retained enzymes within cytosol (>61%), indicating that the INP gene directed the cellulase expression on the bacteria cell surface. Further studies of the optimal enzyme activity were observed at 60 °C and pH 7.0, and at least 75% of maximal enzyme activity was preserved at 70 °C. View Full-Text
Keywords: Bacillus licheniformis; cellulase; ice nucleation protein; Pseudomonas syringae; surface anchoring; whole cell catalysis Bacillus licheniformis; cellulase; ice nucleation protein; Pseudomonas syringae; surface anchoring; whole cell catalysis
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Kim, D.; Ku, S. Bacillus Cellulase Molecular Cloning, Expression, and Surface Display on the Outer Membrane of Escherichia coli. Molecules 2018, 23, 503.

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