Date

2008

Author

Levent, Hande

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This study focuses on the molasses based complex medium design for benzaldehyde lyase production by recombinant E. coli BL21 and development of a feeding strategy based on the designed complex medium. For this purpose, firstly, the effects of molasses were investigated in laboratory scale bioreactors. As E. coli BL21 was not able to utilize sucrose, molasses was pretreated and hydrolyzed to fructose and glucose. Thereafter, effect of pretreated molasses concentration was investigated in the range of 16 to 56 kg m-3 by batch-bioreactor experiments; and the highest cell concentration and benzaldehyde lyase activity were obtained as CX=5.3 kg m-3 and A=1617 U cm-3, respectively, in the medium containing 7.5 kg m-3 glucose and 7.5 kg m-3 fructose. Then, different feeding strategies were developed to produce efficient cells with high concentration and BAL activity. In the first strategy, after 10 hours of batch-cultivation with molasses based medium having 7.5 kg m-3 glucose and 7.5 kg m-3 fructose concentration, based on the airflow rate, pretreated molasses was fed to the system. When air flow rate decreased considerably, fed was given to the system that results in increase in glucose and fructose concentration in the medium to 2.5 kg m-3. At the end of the process, the highest cell concentration obtained was CX=7.4 kg m-3. The maximum activity was reached at 20th hour as A=2360 U cm-3. On the other hand, as air flow variation only demonstrated the absence of glucose not fructose, a second strategy, based on the detection of the fructose and glucose concentrations during the process, was applied. In this strategy when glucose and fructose were depleted, fed was given to the system that results in increase in glucose and fructose concentration in the medium to 2.5 kg m-3; and the highest BAL activity was obtained as 2370 U cm-3 at t= 26 h where the cell concentration was 7.5 kg m-3. At the last strategy, when glucose and fructose were depleted, fed was given to the system that results in increase in CGlucose=1.5 kg m-3 and CFructose=1.5 kg m-3 in the production medium to decrease the accumulation of acetic acid. By this strategy highest cell concentration was obtained as 8.04 kg m-3 at t=24 h and the highest BAL activity was 2315 U cm-3. These strategies could be accepted having the same BAL activity with little distinctions. However, cell concentration of the last one was higher than others and also the lowest amount of carbon source was used. Thus, last one could be chosen as the most favorable strategy.

Subject Keywords

Chemical engineering.

URI

http://etd.lib.metu.edu.tr/upload/3/12609596/index.pdf
https://hdl.handle.net/11511/18269

Collections

Graduate School of Natural and Applied Sciences, Thesis