Enhanced microbial utilization of recalcitrant cellulose by an ex vivo cellulosome-microbe complex.
A cellulosome-microbe complex was assembled ex vivo on the surface of Bacillus subtilis displaying a miniscaffoldin that can bind with three dockerin-containing cellulase components: the endoglucanase Cel5, the processive endoglucanase Cel9, and the cellobiohydrolase Cel48. The hydrolysis performances of the synthetic cellulosome bound to living cells, the synthetic cellulosome, a noncomplexed cellulase mixture with the same catalytic components, and a commercial fungal enzyme mixture were investigated on low-accessibility recalcitrant Avicel and high-accessibility regenerated amorphous cellulose (RAC). The cell-bound cellulosome exhibited 4.5- and 2.3-fold-higher hydrolysis ability than cell-free cellulosome on Avicel and RAC, respectively. The cellulosome-microbe synergy was not completely explained by the removal of hydrolysis products from the bulk fermentation broth by free-living cells and appeared to be due to substrate channeling of long-chain hydrolysis products assimilated by the adjacent cells located in the boundary layer. Our results implied that long-chain hydrolysis products in the boundary layer may inhibit cellulosome activity to a greater extent than the short-chain products in bulk phase. The findings that cell-bound cellulosome expedited the microbial cellulose utilization rate by 2.3- to 4.5-fold would help in the development of better consolidated bioprocessing microorganisms (e.g., B. subtilis) that can hydrolyze recalcitrant cellulose rapidly at low secretory cellulase levels.
Biological Systems Engineering Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA.
Chun
C
You
Xiao-Zhou
XZ
Zhang
Noppadon
N
Sathitsuksanoh
Lee R
LR
Lynd
Y-H Percival
YH
Zhang
D001412:Bacillus subtilis / Q000235:genetics / Q000378:metabolism*; D002482:Cellulose / Q000378:metabolism*; D044603:Cellulosomes / Q000378:metabolism*; D015870:Gene Expression; D006868:Hydrolysis; D060847:Metabolic Engineering
D002482:Cellulose