Engineered Microbial Consortium for the Efficient Conversion of Biomass to Biofuels Page: 29
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interaction between anaerobic bacteria and methanogenic or sulfate-reducing bacteria which
consume hydrogen as it is produced to drive the process forward. An example of this symbiosis is
the breakdown of cadavarine; an aliphatic amine intermediate produced proteinaceous organic
matter degradation [134].
There has been much progress in the development of genetically engineered consortia to
perform unique tasks, and these approaches may be applicable to biofuel-producing consortia
[134]. Shin et al. [140] genetically engineered two E. coli strains for xylan utilization. One strain
was engineered to co-express two hemicellulases to hydrolyze xylan into xylooligosaccharides and
the second imports the xylooligosaccharides to produce ethanol. The ethanol yield for this co-
culture on purified xylan was approximately 55% of the theoretical yield and upon addition of
three purified hemicellulases; a yield of about 71% was achieved suggesting that additional
improvements should be possible by introducing another engineered E. coli strain. Shou et al.
[141] demonstrated a slightly more ideal cooperation using two engineered Saccharomyces
cerevisiae. One strain requires adenine and overproduces lysine while the other requires lysine and
overproduces adenine. In this mutualistic relationship, adenine is released as senescence is
approached which supports the growth of the partner that, in turn, provides the lysine requirement
of the first strain to sustain the dual culture system. In another study by Bayer et al. [142] a
combination of genetic engineering and natural capabilities was used to establish a cooperating
dual culture able to convert cellulose to methyl halides. The cellulolytic bacterium, Actinotalea
fermentans, is inhibited by alcohols and organic acids produced during hydrolysis and
fermentation of cellulose. S. cerevisiae was engineered to utilize these compounds to produce
methyl halides and, when grown in co-culture, alleviated the feedback inhibition on A. fermentans
hydrolysis. The study confirmed that the yeast would not grow on carboxymethyl cellulose without29
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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/m1/40/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .