Biobutanol - Biotechnology in China: Biofuels and Bioenergy - page 93

2.4 New Insights into Genome-Scale Analysis of Physiology
of C. acetobutylicum and Solvent Production
Using Omics Technologies

Omics technologies acting as system biotechnologies have been widely developed
in recent years. Omics study can help understand organisms at the global level.
Many articles have been published on genomics, transcriptomics, proteomics and
metabolomics in C. acetobutylicum [ 1 , 2 , 31 , 39 , 47 ]. After the announcement of
the genome of the typical strain C. acetobutylicum ATCC824 in 2001 by American
researchers, the genome sequences of two other C. acetobutylicum strains

(EA2018 and DSM1731) were also published recently.
C. acetobutylicum EA2018 is a high-butanol-producing, non-spore-forming
strain, generated by N-methyl-N-nitro-N-nitrosoguanidine (NTG) treatment
[ 53 , 54 ]. The butanol ratio and starch conversion rate of the EA2018 strain were
10 and 5% higher, respectively, than the ATCC824 strain [ 7 ]. The size of the
EA2018 chromosome is 650 bp smaller than that of the typical strain ATCC824,
and the size of the EA2018 megaplasmid is 4 bp smaller than that of ATCC824;
in addition, a total of 46 deletion sites and 26 insertion sites were found across
the EA2018 genome, including one deletion site in the megaplasmid [ 22 ].
EA2018 was found to be 99.8% identical to ATCC824, with 72 insertion/dele-
tionss and 451 single nucleotide variations (SNVs), some of which may be
related to the hyper-butanol-producing characteristics of EA2018. Further com-
parative analysis on transcriptomic profiling of gene expression in EA2018 and
ATCC824 revealed increased expression levels of several key genes, such as
spo0A and adhEII. In addition, the variation in CEA_G2622 (CAC2613 in
ATCC824), a putative transcriptional regulator involved in xylose utilization,
may accelerate the utilization of substrate xylose. This information should
be valuable for further genetic modification of C. acetobutylicum to improve
butanol production.
Butanol toxicity is one of the most critical factors affecting ABE fermentation,
and can disrupt the phospholipid components of the cell membrane causing an
increase in membrane fluidity [ 49 ]. It was also found that the cell growth, nutrient
transport and rate of sugar uptake were inhibited and the membrane-bound
ATPase activity was negatively affected by butanol [ 4 , 49 ]. Fermentations of
C. acetobutylicum therefore rarely produce butanol higher than 13 g/L. Mao et al.
used 1% (v/v) diethyl sulfate (DES) mutagenesis and genome shuffling strategies
to generate a mutant strain Rh8 from C. acetobutylicum DSM1731. The mutant
strain Rh8 exhibits enhanced butanol tolerance of 19 g/L, and could grow in the
presence of 18 g/L butanol, compared with the severe inhibition of strain
DSM1731 by 12 g/L butanol. In pH control batch fermentation, the production of
acetone and butanol in Rh8 increased by 18 and 23% respectively compared to
DSM1731. Compared with the genome sequence of C. acetobutylicum strain
ATCC824 and EA2018, the strain DSM1731 has 11.1 kb plasmid, pSMBb, which
has not been previously reported in this species. 345 SNVs were identified between