Engineered Microbial Consortium for the Efficient Conversion of Biomass to Biofuels Page: 13
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DNA conferred the ability to co-ferment mannose and glucose producing 91% of the theoretical
yield of ethanol within 36 h. They further introduced a recombinant plasmid harboring the genes
encoding E. coli xylA, xylB, tal and tktA and broadened the range of fermentable sugar substrates
for Z. mobilis to include mannose and xylose as well as glucose with 89.8% theoretical yield of
ethanol within 72 hours. The /l-glucosidase gene from Xanthomonas albilneans or Ruminococcus
albus was expressed in Z. mobilis [56, 57]. Yanase et al. [56] expressed a/i-glucosidase gene from
Ruminococcus albus fused with the Tat (twin arginine translocation) signal peptide of a
periplasmic enzyme, glucose-fructose oxidoreductase (Gfor), or Sec-dependent secretion signal
peptide of gluconolactonase (Gln). They found that the enzyme thus produced was secreted into
both the periplasmic and extracellular space. With the Tat and Sec signal peptides, 4.7% and 11.2%
of the 8-glucosidase activity, respectively, were detected in the extracellular space of the
recombinant Z. mobilis. However, these genes could not support the growth of recombinant Z.
mobilis on cellobiose as the sole carbon source. Linger et al. [58] heterologously expressed two
cellulolytic enzymes El (endo-i- 1, 4-glucanase) and GH12 (broad substrate range endofl- 1,4-
glucanase activity) from an Acidothermus species by using two different secretion signals of Z.
mobilis genes, phoC gene and ORFZM0331. The lack of a secretion signal in their gene resulted
in the localization of 96% of GH12 activity within the cytoplasm, whereas the addition of the phoC
secretion signal resulted in the localization of approximately 26% of the enzyme activity in the
periplasmic space and 13% in the extracellular space. For El with the phoC secretion signal,
approximately 20% of the El activity was found in the extracellular medium, 30% in the
periplasmic space and 50% in cytoplasm. To develop Z. mobilis as a viable platform host organism
for cellulosic biofuel production, more studies are needed to engineer strains that secrete multiple
PCDEs into the extracellular space necessary for the degradation of plant biomass [44].13
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Anieto, Ugochukwu Obiakornobi. Engineered Microbial Consortium for the Efficient Conversion of Biomass to Biofuels, dissertation, August 2014; Denton, Texas. (https://digital.library.unt.edu/ark:/67531/metadc699973/m1/24/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .