CONICET | Buscador de Institutos y Recursos Humanos

Lactic acid bacteria (LAB) and yeasts have been used for years in bread making to improve the dough properties and bread characteristics. Sucrose, a disaccharide composed of glucose and fructose, represents 1% of the soluble carbohydrates in wheat flour. This sugar is metabolized by the microorganisms having invertase (ß-D fructofuranoside fructohydrolase), an occasional enzyme in LAB. In previous studies, the invertase of Lactobacillus reuteri CRL 1100 of sourdough origen was purified and characterized. In response to changes in the dough ecosystem, the enzymes biosynthesis has to be regulated. The aim of this study was to determine the regulation of the invertase synthesis in Lb. reuteri CRL 1100. The effect of monosaccharides (glucose, fructose, galactose), disaccharides (maltose, sucrose and melibiose) and trisaccharide (raffinose) was determined. Results indicate that the enzyme expression took place in the presence of raffinose and sucrose, specific substrates, indicating that the enzyme is substrate inducible. On the contrary, glucose and fructose, final products of the invertase activity, repressed the enzyme activity by 64% and 26%, respectively. The cAMP addition did not affect the invertase repression by glucose or fructose indicating that the catabolic repression by these monosaccharides was cAMP independent. In presence of sucrose, glucose and fructose, the inhibition of invertase synthesis was less respect to sucrose plus glucose, suggesting that fructose could protect the enzyme from the glucose inhibition. The de novo enzyme synthesis was inhibited (96% and 73%) by rifampicin and chloramphenicol, respectively. These results indicate that the enzyme induction would be mainly regulated at the transcription level.