Skip to Main Content
 

Global Search Box

 
 
 

ETD Abstract Container

Abstract Header

Metabolic Engineering of Propionibacteria for Enhanced Propionic Acid and n-Propanol Fermentative Production

Ammar, Ehab Mohamed
http://rave.ohiolink.edu/etdc/view?acc_num=osu1374174278

Abstract Details

2013, Doctor of Philosophy, Ohio State University, Biochemistry.
Propionibacteria are widely used in industry for manufacturing of Swiss cheese, vitamin B12 and propionic acid. However, little is known about their genetics and only a few reports are available on their metabolic engineering aiming at enhancing production of vitamin B12 and propionic acid. The latter is widely used as a chemical intermediate in various manufacturing processes, and its salts are common food preservatives. It is currently produced via petrochemicals, but there is increasing interest in its fermentative production from renewable biomass. However, current propionic acid fermentation process suffers from low product yield and productivity. n-Propanol is a common solvent, an intermediate in many industrial applications and a promising biofuel. To date, no wild-type microorganism is known to produce n-propanol in sufficient quantities for industrial purposes. However, some attempts to produce n-propanol in E. coli and S. cerevisiae have been reported, but the yields and titers are still unsatisfactory. In this study, a bifunctional aldehyde/alcohol dehydrogenase (adhE) was cloned from E. coli and expressed in P. freudenreichii. The mutants expressing the adhE gene converted propionyl-CoA, which is the precursor for propionic acid biosynthesis, to n-propanol. The production of n-propanol was limited by NADH availability, which was improved significantly by using glycerol as the carbon source. Interestingly, the improved propanol production was accompanied by a significant increase in propionic acid productivity, indicating a positive effect of n-propanol biosynthesis on propionic acid fermentative production. To our best knowledge, this is the first report on producing n-propanol by metabolically engineered propionibacteria, which offers a novel route to produce n-propanol from renewable feedstock, and possibly a new way to boost propionic acid fermentation. In this work, another gene was also expressed in Propionibacterium freudenreichii. Its expression in P. freudenreichii resulted in profound effects on propionic acid fermentation. Compared to the wild type, the mutant showed better propionate production kinetics. These effects could be attributed to changes in the flux distributions in the dicarboxylic acid pathway. Promoters are key elements in metabolic engineering as they control the level of gene expression. Some strong promoters from P. freudenreichii have been reported. To our best knowledge, no report is available on analyzing promoter strengths from P. acidipropionici. Therefore, eleven promoters from P. acidipropionici ATCC 4875 were cloned into a shuttle vector with a promoterless reporter gene and transformed into the host. Promoter strengths were analyzed as function of the reporter gene activity. Results showed that these promoters were able to enforce expression of the reporter gene to different levels in propionibacteria. In addition, sequence analysis showed that promoters from P. acidipropionici were more complicated than those from regular prokaryotes, and hence more investigations are needed in this area. These findings should contribute towards improving future metabolic engineering of P. acidipropionici for enhanced propionic acid fermentation.
Shang-Tian Yang (Advisor)
Ross Dalbey (Committee Member)
Jeffrey Chalmers (Committee Chair)
182 p.
Biochemistry; Chemical Engineering; Microbiology
Propionibacteria, Propionic acid, Propanol, Metabolic engineering, Biotechnology

Recommended Citations

Citations

  • Ammar, E. M. (2013). Metabolic Engineering of Propionibacteria for Enhanced Propionic Acid and n-Propanol Fermentative Production [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1374174278

    APA Style (7th edition)

  • Ammar, Ehab. Metabolic Engineering of Propionibacteria for Enhanced Propionic Acid and n-Propanol Fermentative Production. 2013. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1374174278.

    MLA Style (8th edition)

  • Ammar, Ehab. "Metabolic Engineering of Propionibacteria for Enhanced Propionic Acid and n-Propanol Fermentative Production." Doctoral dissertation, Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1374174278

    Chicago Manual of Style (17th edition)

osu1374174278
1,417
© 2013, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.
Release 3.2.12