Journal
BIOTECHNOLOGY FOR BIOFUELS
Volume 7, Issue -, Pages -Publisher
BMC
DOI: 10.1186/1754-6834-7-112
Keywords
Designer cellulosome; Biomass; Bioprocessing; Wheat straw; Glycoside hydrolase; Enzymatic paradigm; Spatial differentiation; Biomimicry
Funding
- Israel Ministry of Science Technology and Space [362043313]
- Israel Ministry of Agriculture and Rural Development [362042613]
- Sidney E Frank Foundation through the Israel Science Foundation (ISF) [24/11]
- Research Fund of Israel Dairy Board [362-0348-12362-0316-11]
- ISF [1325/14]
- Israeli Center of Research Excellence (I-CORE Center [152/11]
- United States-Israel Binational Science Foundation (BSF), Jerusalem, Israel
- Weizmann Institute of Science Alternative Energy Research Initiative (AERI)
- Helmsley Foundation
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Background: Lactobacillus plantarum is an attractive candidate for metabolic engineering towards bioprocessing of lignocellulosic biomass to ethanol or polylactic acid, as its natural characteristics include high ethanol and acid tolerance and the ability to metabolize the two major polysaccharide constituents of lignocellulolytic biomass (pentoses and hexoses). We recently engineered L. plantarum via separate introduction of a potent cellulase and xylanase, thereby creating two different L. plantarum strains. We used these strains as a combined cell-consortium for synergistic degradation of cellulosic biomass. Results: To optimize enzymatic degradation, we applied the cell-consortium approach to assess the significance of enzyme localization by comparing three enzymatic paradigms prevalent in nature: (i) a secreted enzymes system, (ii) enzymes anchored to the bacterial cell surface and (iii) enzymes integrated into cellulosome complexes. The construction of the three paradigmatic systems involved the division of the production and organization of the enzymes and scaffold proteins into different strains of L. plantarum. The spatial differentiation of the components of the enzymatic systems alleviated the load on the cell machinery of the different bacterial strains. Active designer cellulosomes containing a xylanase and a cellulase were thus assembled on L. plantarum cells by co-culturing three distinct engineered strains of the bacterium: two helper strains for enzyme secretion and one producing only the anchored scaffoldin. Alternatively, the two enzymes were anchored separately to the cell wall. The secreted enzyme consortium appeared to have a slight advantage over the designer cellulosome system in degrading the hypochlorite pretreated wheat straw substrate, and both exhibited significantly higher levels of activity compared to the anchored enzyme consortium. However, the secreted enzymes appeared to be less stable than the enzymes integrated into designer cellulosomes, suggesting an advantage of the latter over longer time periods. Conclusions: By developing the potential of L. plantarum to express lignocellulolytic enzymes and to control their functional combination and stoichiometry on the cell wall, this study provides a step forward towards optimal biomass bioprocessing and soluble fermentable sugar production. Future expansion of the preferred secreted-enzyme and designer-cellulosome systems to include additional types of enzymes will promote enhanced deconstruction of cellulosic feedstocks.
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