Fructose induces gene expression of mannitol 2-dehydrogenase of Lactobacillus reuteri CRL 1101

ORTIZ, M.E.; BLECKWEDEL, J.; HEBERT, E.M.; FERRANTI, P.; PICARIELLO, G.; RAYA, R.R.; MOZZI, F.

Simposio; 11th International Symposium on Lactic Acid Bacteria. HEALTH, SUSTAINABILITY, DIVERSITY, AND APPLICATION; 2014

Mannitol, a polyol produced by certain heterofermentative lactic acid bacteria, has multiple industrial applications, being mainly used as natural sweetener in the food industry due to its low-caloric, low-glycemic, and anti-cariogenic properties. Under certain culture conditions these microorganisms may use fructose as an alternative electron acceptor to produce mannitol using the mannitol 2-dehydrogenase (MDH) enzyme. We aimed to investigate the effect of fructose on mRNA mdh expression, MDH synthesis and activity, as well as mannitol production by Lactobacillus reuteri CRL1101. The strain was grown in a chemically defined medium (CDM) with 2% glucose and 5% fructose (CDMF) as carbon sources at 37 °C for 24 h. CDM with 7% glucose (CDMG) was used as control. Cell growth (CFU/mL), pH, mannitol production and residual sugar concentration (HPLC), mdh gene expression (qPCR), MDH synthesis (2D-PAGE) and activity (spectrophotometrically) were determined. Lb. reuteri CRL1101 produced 20 g mannitol/L in CDMF after 24 h-incubation. Although no mannitol was detected in CDMG, basal MDH activity values were 0.5 ± 0.1 U/mg prot at all assayed time points were obtained. In presence of fructose, a 6-fold increase in MDH activity (3.0 ± 0.2 U/mg prot) was found after 8 h-incubation compared to the control. Interestingly, mdh gene expression was 55-fold higher in CDMF than in CDMG at the same incubation time. This observation is consistent with differential MDH expression as a clear proteomic spot at 8 h-incubation in CDMF but not in CDMG was detected. Our findings demonstrate that the presence of fructose highly induces mdh gene and protein expression in Lb. reuteri CRL 1101.