Genetic engineering to improve butanol tolerance High
butanol concentration is known as a potent inhibitor to the growth
of the microorganism, as butanol tends to partition into the cytoplasmic
membrane and changes the membrane structure, thereby
interfering with its normal function (5). Therefore, it is essential to
reduce the sensitivity of butanol-producing strains to butanol.
Overexpression of Spo0A in C. acetobutylicum resulted in increased
tolerance and prolonged metabolism in response to butanol stress
(67). Similarly, overexpression of groESL, which belongs to the
class I heat shock protein genes in C. acetobutylicum, improved
butanol tolerance because the groESL gene prevented aggregation
and assisted in protein folding under butanol stress (65). Reyes
et al. (68) used a genomic library enrichment strategy to screen
genes involved in butanol tolerance in Escherichia coli.
Overexpression of entC, which encodes isochorismate synthase,
and feoA, which encodes a small protein that is involved in iron
transport, increased butanol tolerance by 32.8% and 49.1%,
respectively. In contrast, deletion of the astE gene, which encodes
a protein that belongs to the succinylglutamate desuccinylase/
aspartoacylase family, resulted in a 48.7% increase in butanol
resistance (68). In addition to E. coli, Lactobacillus strains were
found to tolerate and grow in up to 3% butanol (69). Moreover,
adapted Pseudomonas putida strains were reported to grow in the
presence of up to 6% butanol, which was the highest butanol
concentration tolerated by the microorganisms (70). Although the above-described genetically engineered butanol-tolerant strains
were capable of producing butanol, the concentration and yield of
butanol were relatively low.
Genetic engineering to improve butanol tolerance High
butanol concentration is known as a potent inhibitor to the growth
of the microorganism, as butanol tends to partition into the cytoplasmic
membrane and changes the membrane structure, thereby
interfering with its normal function (5). Therefore, it is essential to
reduce the sensitivity of butanol-producing strains to butanol.
Overexpression of Spo0A in C. acetobutylicum resulted in increased
tolerance and prolonged metabolism in response to butanol stress
(67). Similarly, overexpression of groESL, which belongs to the
class I heat shock protein genes in C. acetobutylicum, improved
butanol tolerance because the groESL gene prevented aggregation
and assisted in protein folding under butanol stress (65). Reyes
et al. (68) used a genomic library enrichment strategy to screen
genes involved in butanol tolerance in Escherichia coli.
Overexpression of entC, which encodes isochorismate synthase,
and feoA, which encodes a small protein that is involved in iron
transport, increased butanol tolerance by 32.8% and 49.1%,
respectively. In contrast, deletion of the astE gene, which encodes
a protein that belongs to the succinylglutamate desuccinylase/
aspartoacylase family, resulted in a 48.7% increase in butanol
resistance (68). In addition to E. coli, Lactobacillus strains were
found to tolerate and grow in up to 3% butanol (69). Moreover,
adapted Pseudomonas putida strains were reported to grow in the
presence of up to 6% butanol, which was the highest butanol
concentration tolerated by the microorganisms (70). Although the above-described genetically engineered butanol-tolerant strains
were capable of producing butanol, the concentration and yield of
butanol were relatively low.
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