Mannitol production and mannitol 2-dehydrogenase activity are induced by fructose during early growth of Lactobacillus reuteri CRL1101 in rich and chemically defined media

MARIA EUGENIA, ORTIZ, RAÚL R., RAYA, FERNANDA, MOZZI

Cardiff, UK

Conferencia; SfAM Summer Conference 2013; 2013

Society for Applied Microbiology-SfAM

Aims Mannitol, a polyol produced by certain heterofermentative lactic acid bacteria, has multiple industrial applications due to its low-caloric, low-glycemic and anti-cariogenic properties. We aimed to investigate mannitol production and the activity of mannitol 2-dehydrogenase (MDH), an enzyme responsible for reducing fructose into mannitol, in Lactobacillus reuteri CRL1101 using rich and chemically defined media (CDM). Methods and results To induce mannitol formation by L. reuteri CRL1101, fructose (5%, w/v) was added at different growth phases of cultures (lag: 1 h, log: 6 h, stationary: 10 h) grown in MRS and incubated at 37°C. Cell growth (CFU/ml), pH, mannitol production and residual sugar concentration (HPLC), and MDH activity were determined. The highest mannitol production (30.9±2.6 g/l) was obtained at 24 h when fructose was added during the lag or log growth phase. The highest MDH activity value (1.9±0.1 U/mg prot) was found after 8 h of incubation when fructose was available in the log phase. This MDH value was 2.4-fold higher than that found in MRS without fructose (0.8±0.3 U/mg prot). Induction of MDH by fructose was studied in a CDM; using a glucose-supplemented CDM as a control. Mannitol production by the L. reuteri strain was 1.6-fold lower in CDM than in MRS with fructose after 24 h. However, an increase in the MDH activity (3.0±0.2 U/mg prot) was observed after 8 h of incubation as compared with CDM-glucose (0.5±0.2 U/mg prot) and MRS-fructose. Conclusions Maximal mannitol production by L. reuteri CRL1101 occurred when fructose was available in the culture medium during early growth phase. MDH was highly induced by fructose, but a low constitutive activity was displayed by the strain. Significance of study Knowledge on fructose utilization by L. reuteri CRL1101 and on MDH activity is crucial for improving mannitol production by this strain.