| Butanol is not only an important chemical material used for synthesizing various chemicals, but also a promising biofuel. Compared with bioethanol, butanol has higher combustion value, lower vapor pressure and a broader application prospect. However, current industrial ABE fermentation process is limited by butanol toxicity, which leads to deficiency, such as low convert ratio, low productivity and low yield. In this study, we have used strain Clostridium saccharobutylicum DSM 13864 was used. The whole genome of C. saccharobutylicum was extracted and sequenced. Brick was chosen as immobilization materials in ABE fermentation, and the process was also coupled with gas stripping to improve butanol yield and productivity.The genome of C. saccharobutylicum DSM 13864 comprises of 4,969,249 bases with a GC content of 28.38% and forecasted 4,472 genes. The forecasted genes were compared with NR database of NCBI, and 4,175 genes were identified, among which, 3,299 genes have unambiguous function, 3,141 protein have COG classification, and those matched proteins were derived from 676 species, 21.82% matched proteins are matched with Clostridium sp. Maddingley MBC34-26. In addition, 1,596 metabolic pathways were constructed based on KEGG database, and the genomic information provide clear genetic background for future strain improvement.The microbial adhesion to solvents(MATS) cells collected at two different growth stages displayed the highest affinity to chloroform, an electron-acceptor solvent, and relatively lower affinity for ethyl acetate, an electron-donor solvent. With regard to hexadecane and decane, two nonpolar solvents, lower affinity was observed. All the results show that cell surface of C. saccharobutylicum is highly hydrophilic and may act as a strong electron donor, as well as a moderate electron acceptor. Electrophoretic mobilities showed the isoelectric point was determined to be p H 3, and the cells were negatively charged at p H values of above 3. Hydrophilic C. saccharobutylicum cells are capable of adhering in large numbers to brick, a hydrophilic support.Using 60 g 5~8 mesh brick in 150 m L medium, solvents reached the highest concentrations: butanol 11.1 g·L-1 and total solvents 16.0 g·L-1 were reached, presenting 15.6% and 17.6 % increase compared with those of the control(free cells). Scanning of electron microscope shows large amount of cells were adsorbed onto the support materials and almost completely covered the surface of porous brick. In addition, 10 batch cycles were consecutively performed to test the adsorptive stability. After 480 h fermentation, butanol and total solvents could maintain at above 10 g·L-1 and 15 g·L-1 respectively, indicating C. saccharobutylicum cells adsorbed on the brick surface can keep vitality during the 20-day process.In a 3-L bioreactor equipped with an immobilization device at a flow rate of 1.1 g·L-1, the final concentration of butanol and total solvents are 11.02 g·L-1 and 16.55 g·L-1, improved 12.12% and 6.80% compared with the control. When ABE fermentation coupled with gas stripping, the productivity and yield of butanol are 0.222 g·L-1·h-1 and 0.177 g·g-1, improved 7.25% and 6.62% compared with the control. When the immobilized fermentation process is coupled with gas stripping, the yield of butanol and total solvent are 0.191 g·g-1 and 0.281 g·g-1, presenting 15.06% and 8.49% increase. |
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