Present addresses I. Díaz-Muñiz, United States Department of Agriculture, Agricultural Research Services, Food Science Research Unit, North Carolina State University, 322 Schaub Hall, Campus Box 7624, Raleigh, North Carolina 27695-7624, USA.
Lactobacillus casei metabolic potential to utilize citrate as an energy source in ripening cheese: a bioinformatics approach
Article first published online: 27 JUN 2006
Journal of Applied Microbiology
Volume 101, Issue 4, pages 872–882, October 2006
How to Cite
Díaz-Muñiz, I., Banavara, D.S., Budinich, M.F., Rankin, S.A., Dudley, E.G. and Steele, J.L. (2006), Lactobacillus casei metabolic potential to utilize citrate as an energy source in ripening cheese: a bioinformatics approach. Journal of Applied Microbiology, 101: 872–882. doi: 10.1111/j.1365-2672.2006.02965.x
E.G. Dudley, University of Maryland-School of Medicine, 685 W. Baltimore St., Room 447, Baltimore, MD 21201, USA.
- Issue published online: 30 AUG 2006
- Article first published online: 27 JUN 2006
- 2005/0731: received 25 June 2005, revised 20 December 2005 and accepted 6 February 2006
- Cheddar cheese extract;
- citrate catabolism;
- lactic acid bacteria;
Aims: To identify potential pathways for citrate catabolism by Lactobacillus casei under conditions similar to ripening cheese.
Methods and Results: A putative citric acid cycle (PCAC) for Lact. casei was generated utilizing the genome sequence, and metabolic flux analyses. Although it was possible to construct a unique PCAC for Lact. casei, its full functionality was unknown. Therefore, the Lact. casei PCAC was evaluated utilizing end-product analyses of citric acid catabolism during growth in modified chemically defined media (mCDM), and Cheddar cheese extract (CCE). Results suggest that under energy source excess and limitation in mCDM this micro-organism produces mainly l-lactic acid and acetic acid, respectively. Both organic acids were produced in CCE. Additional end products include d-lactic acid, acetoin, formic acid, ethanol, and diacetyl. Production of succinic acid, malic acid, and butanendiol was not observed.
Conclusions: Under conditions similar to those present in ripening cheese, citric acid is converted to acetic acid, l/d-lactic acid, acetoin, diacetyl, ethanol, and formic acid. The PCAC suggests that conversion of the citric acid-derived pyruvic acid into acetic acid, instead of lactic acid, may yield two ATPs per molecule of citric acid. Functionality of the PCAC reductive route was not observed.
Significance and Impact of the Study: This research describes a unique PCAC for Lact. casei. Additionally, it describes the citric acid catabolism end product by this nonstarter lactic acid bacteria during growth, and under conditions similar to those present in ripening cheese. It provides insights on pathways preferably utilized to derive energy in the presence of limiting carbohydrates by this micro-organism.