Lignocellulosic biomass represents a promising renewable alternative to fossil fuels for sustainable production of chemicals, materials, and biofuels
1. However, the heterogeneous and recalcitrant nature of lignocellulosic polymers presents a technical blocker for industrial exploitation of plant biomass
2. One potential solution to this problem is the development of whole cell biocatalysts engineered for scalable conversion of lignocellulosic biomass into valuable products. To this end, we have developed efficient high-throughput metagenomic approaches for the discovery of biomass deconstruction processes in natural ecosystems including biocatalysts for cellulose, hemicellulose and lignin
3,4. These biocatalysts can be arrayed in different combinations supporting consolidated bioprocessing based on S-layer display on the cell surface of
Caulobacter crescentus5. We specifically chose the
Caulobacter S-layer as an expression and display platform, because the layer is composed of a single rsaA protein constituting ~10% of the total protein in
Caulobacter6. Fusion of catalytic enzymes to the rsaA protein facilitates a highly efficient display of multiple copies of biocatalysts per cell enabling development of whole-cell biocatalysts. We validated this approach by displaying characterized cellulases, such as CEX, E1, Endo5A and Gluc1C
7,8 on the cell surface of
C.crescentus and assaying for the capacity to convert cellulose to simple sugars for growth. We are currently adapting this approach to display a wide range of biocatalysts for cellulose, hemicellulose and lignin discovered in functional metagenomic screens for whole cell combinatorial biomass conversion processes. In parallel, we have initiated the development of synthetic microbial communities comprised of engineered
C. crescentus displaying different biocatalysts to produce sugars that can be funneled into defined biosynthetic pathways when co-cultured with
E. coli. The resulting synthesis platform can be tuned to local biomass sources and operational conditions for consolidated bioprocessing of lignocellulosic biomass.
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4. Strachan, C. R. et al. Metagenomic scaffolds enable combinatorial lignin transformation. Proc. Natl. Acad. Sci. U. S. A. 111,10143–8 (2014).
5. Bingle, W. H., Nomellini, J. F. & Smit, J. Cell-surface display of a Pseudomonas aeruginosa strain K pilin peptide within the paracrystalline S-layer of Caulobacter crescentus. Mol. Microbiol. 26,277–288 (1997).
6. Ho, J., Lau, Y., Nomellini, J. F. & Smit, J. Analysis of high-level S-layer protein secretion in Caulobacter crescentus. 514,501–514 (2010).
7. Gupta, S., Adlakha, N. & Yazdani, S. S. 2013-Efï¬cient extracellular secretion of an endoglucanase and a b-glucosidase in E. coli.pdf. 88,20–25 (2013).
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