Expression of naturally ionic liquid-tolerant thermophilic cellulases in Aspergillus niger

PLoS One. 2017 Dec 27;12(12):e0189604. doi: 10.1371/journal.pone.0189604. eCollection 2017.

Abstract

Efficient deconstruction of plant biomass is a major barrier to the development of viable lignocellulosic biofuels. Pretreatment with ionic liquids reduces lignocellulose recalcitrance to enzymatic hydrolysis, increasing yields of sugars for conversion into biofuels. However, commercial cellulases are not compatible with many ionic liquids, necessitating extensive water washing of pretreated biomass prior to hydrolysis. To circumvent this issue, previous research has demonstrated that several thermophilic bacterial cellulases can efficiently deconstruct lignocellulose in the presence of the ionic liquid, 1-ethyl-3-methylimadizolium acetate. As promising as these enzymes are, they would need to be produced at high titer in an industrial enzyme production host before they could be considered a viable alternative to current commercial cellulases. Aspergillus niger has been used to produce high titers of secreted enzymes in industry and therefore, we assessed the potential of this organism to be used as an expression host for these ionic liquid-tolerant cellulases. We demonstrated that 29 of these cellulases were expressed at detectable levels in a wild-type strain of A. niger, indicating a basic level of compatibility and potential to be produced at high levels in a host engineered to produce high titers of enzymes. We then profiled one of these enzymes in detail, the β-glucosidase A5IL97, and compared versions expressed in both A. niger and Escherichia coli. This comparison revealed the enzymatic activity of A5IL97 purified from E. coli and A. niger is equivalent, suggesting that A. niger could be an excellent enzyme production host for enzymes originally characterized in E. coli, facilitating the transition from the laboratory to industry.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Aspergillus niger / enzymology*
  • Biomass
  • Cellulases / genetics
  • Cellulases / metabolism*
  • Escherichia coli / genetics
  • Fermentation
  • Hydrolysis
  • Ionic Liquids / metabolism*
  • Recombinant Proteins / metabolism

Substances

  • Ionic Liquids
  • Recombinant Proteins
  • Cellulases

Grants and funding

This work was conducted within the U.S. Department of Energy (DOE) Joint BioEnergy Institute (http://www.jbei.org), which is supported by DOE’s Office of Science, Office of Biological and Environmental Research, under contract DE-AC02-05CH11231 with Lawrence Berkeley National Laboratory. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Three authors currently reside at Proteus Digital Health, Inc. Redwood City, CA, or Ginkgo Bioworks, Inc. Boston, MA, or Corning Inc, Corning, NY, USA. All work reported in this manuscript was conducted prior to the authors employment at these companies and neither Proteus Digital Health, Inc., Ginkgo Bioworks, Inc., nor Corning Inc provided support in the form of salaries for any of the authors, and they did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.