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Issue 8, 2011
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Identification of a haloalkaliphilic and thermostable cellulase with improved ionic liquid tolerance

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Abstract

Some ionic liquids (ILs) have been shown to be very effective solvents for biomass pretreatment. It is known that some ILs can have a strong inhibitory effect on fungal cellulases, making the digestion of cellulose inefficient in the presence of ILs. The identification of IL-tolerant enzymes that could be produced as a cellulase cocktail would reduce the costs and water use requirements of the IL pretreatment process. Due to their adaptation to high salinity environments, halophilic enzymes are hypothesized to be good candidates for screening and identifying IL-resistant cellulases. Using a genome-based approach, we have identified and characterized a halophilic cellulase (Hu-CBH1) from the halophilic archaeon, Halorhabdus utahensis. Hu-CBH1 is present in a gene cluster containing multiple putative cellulolytic enzymes. Sequence and theoretical structure analysis indicate that Hu-CBH1 is highly enriched with negatively charged acidic amino acids on the surface, which may form a solvation shell that may stabilize the enzyme, through interaction with salt ions and/or water molecules. Hu-CBH1 is a heat tolerant haloalkaliphilic cellulase and is active in salt concentrations up to 5 M NaCl. In high salt buffer, Hu-CBH1 can tolerate alkali (pH 11.5) conditions and, more importantly, is tolerant to high levels (20% w/w) of ILs, including 1-allyl-3-methylimidazolium chloride ([Amim]Cl). Interestingly, the tolerances to heat, alkali and ILs are found to be salt-dependent, suggesting that the enzyme is stabilized by the presence of salt. Our results indicate that halophilic enzymes are good candidates for the screening of IL-tolerant cellulolytic enzymes.

Graphical abstract: Identification of a haloalkaliphilic and thermostable cellulase with improved ionic liquid tolerance

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Publication details

The article was received on 21 Feb 2011, accepted on 08 Apr 2011 and first published on 01 Jul 2011


Article type: Paper
DOI: 10.1039/C1GC15193B
Citation: Green Chem., 2011,13, 2083-2090
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    Identification of a haloalkaliphilic and thermostable cellulase with improved ionic liquid tolerance

    T. Zhang, S. Datta, J. Eichler, N. Ivanova, S. D. Axen, C. A. Kerfeld, F. Chen, N. Kyrpides, P. Hugenholtz, J. Cheng, K. L. Sale, B. Simmons and E. Rubin, Green Chem., 2011, 13, 2083
    DOI: 10.1039/C1GC15193B

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