better alternatives of corn, sugarcane for ethanol production (Balat and Balat 2009;
Rogers et al. 2007).
6.11 Strategies for Strain Improvement of Z. mobilis
Now there is demand of renewable resources, sustainable biofuels technologies, and
lignocellulose substrates to obtain high yield of biofuel. The strategies adopted are:
6.11.1 Conventional Mutagenesis
Selective mutants of Z. mobilis were made using mutagenic agents like caffeine,
EMS (ethyl methane sulfonate), UV lights, etc., for bioethanol industry. Mutants of
Z. mobilis obtained were auxotrophic, osmotolerant, sucrose-hyper tolerant,
fructose-negative, and antibiotic sensitive strains which showed desired applications
in bioethanol industry (Wang et al. 2013).
6.11.2 Transposon Mutagenesis
This is successfully done by using broad host range plasmids like Tn951, Tn5,
(Wang et al. 2013) and Tn1725 using Z. mobilis. Carey et al. (1983) stated that
plasmid PGC91.14 successfully expressed in Z. mobilis at 30
C. Transposon
mutagenesis is an effective tool for the ethanol production. Using TN5 transposed
Z. mobilis recombinant plasmid replicon fusions were also helpful (Zhang et al.
2013).
6.11.3 Adaptive Laboratory Evolution (ALE)
This is effective for strains optimization selection and adaption. Metabolic engineering is also helpful (Zheng et al. 2009). Selective mutants were made using adaptive
mutation protocols for the bioethanol production. Agrawal et al. followed these
protocols for the xylose-fermenting Z. mobilis. Substrate utilization and inhibitor
tolerance are limitations and can be overcome by using mutants made from ALE
procedures (Kerr et al. 2011).
6 Engineering of Zymomonas mobilis for Enhanced Biofuel Production
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