(63f) Engineering E. Coli Whole-Cell Catalysts for Consolidated Production of Lactic Acid From Cellodextrin

            Engineering E. coli whole-cell catalysts
for consolidated production of lactic acid from cellodextrin

Charles Rutter, Nimmy
Mathew, Rachel Chen

School of Chemical
and Biomolecular Engineering, Georgia Institute of Technology

Reduction of production cost for
bio-based fuels and chemicals is an important engineering objective yet to be
achieved. Consolidated bioprocessing is one of the approaches being pursued by
many laboratories around the globe and offers an opportunity for significant
cost reduction by combining cellulase production, cellulose depolymerization,
and product synthesis in a single step. Engineering microbial catalyst capable
of performing these three tasks is, however, challenging. As a consequence,
consolidated processing remains largely laboratory adventures, despite
significant progresses in the past few years.

In order to develop a system to be used for consolidated
bioprocessing of cellulose, expression and secretion of β-glucosidase and
cellodextrinase must be achieved.  This presentation describes the use of a
heterologous cellodextrinase to enable E. coli cells to grow on
cellodextrins and cellobiose.  This enzyme has been shown to release glucose
from cello-oligomers across a range of degrees of polymerization with highest
activity on cellotetraose.  Additionally, we have shown that this heterologous
lipoprotein is properly transolcated, acylated, and inner membrane associated
in the E. coli host.  Finally, periplasmic displayed enzyme conferred
the cells  the ability to metabolize cellodextrins and ferment them to lactic
acid at nearly 75% of theoretical yield.

            This study marks the first attempt at using an
inner membrane anchored lipoprotein as an enzyme for degradation of substrates
located in the extracellular medium. The ability of this enzyme to hydrolyze
extracellular without being translocated across the outer membrane helps to reduce
the energetic requirements of this strain for use in consolidated
bioprocesses.  Additionally, this study demonstrates that heterologous
lipoproteins can be properly modified post-translationally by E. coli
and localized to the periplasmic space.