Catabolite repression of <i>Pediococcus halophilus</i>

Old soya sauce becomes dark brown!: Soya sauce is rich in amino acids and also contains pentoses. Amino acids and sugars, especially pentoses, react to form pigments.; Soya sauce is a fermentation product of soya beans by Pediococcus halophilus. Even a bacterium has its taste for sugars. It likes glucose and fructose (hexoses) the best, and after complete consumption of such hexoses, it finally manages to utilize pentoses. Thus, pentoses usually remain unutilized in the fermentation product. This preference for hexoses is called "glucose effect" or "catabolite regulation". And this is the cause of the colour of old soya sauce.
How to manage this trouble?
How to manage this trouble?: We have cloned the xylose(a pentose) utilization genes from Pediococcus halophilus. Sequencing of the genes revealed the regulatory system of this gene expression (catabolite repression). Then we disrupt responsible regulatory genes for this catabolite repression by site-directed mutagenesis.
What we have done

Purification of HPr protein in phosphoenolpyruvate dependent sugar phosphotransferase system
　　Arai et al., Biochem. Int. 27, 275-279 (1992)
Cloning and sequencing of xylose utilization genes and elucidation of the regulatory mechanism of gene expression of the xylose utilization operon
　　Takeda et al., Appl. Environ. Microbiol. 64, 2513-2519 (1998)

Molecular mechanism of the regulation of xyl operon expression and site-directed mutations of the regulatory network
Finally, making a delicious soya sauce

Old soya sauce becomes dark brown!