Efficient mannitol production by wild-type Lactobacillus reuteri CRL 1101 is attained at constant pH using a simplified culture medium

Abstract

Mannitol is a natural polyol with multiple industrial applications. In this work, mannitol production by Lactobacillus reuteri CRL 1101 was studied at free- and controlled-pH (6.0-4.8) fermentations using a simplified culture medium containing yeast and beef extracts and sugarcane molasses. The activity of mannitol 2-dehydrogenase (MDH), the enzyme responsible for mannitol synthesis, was determined. The effect of the initial biomass concentration was further studied. Mannitol production (41.5 ± 1.1 g/l), volumetric productivity (Q Mtl 1.73 ± 0.05 g/l h), and yield (Y Mtl 105 ± 11 %) were maximum at pH 5.0 after 24 h while the highest MDH activity (1.66 ± 0.09 U/mg protein) was obtained at pH 6.0. No correlation between mannitol production and MDH activity was observed when varying the culture pH. The increase (up to 2000-fold) in the initial biomass concentration did not improve mannitol formation after 24 h although a 2-fold higher amount was produced at 8 h using 1 or 2 g cell dry weight/l comparing to the control (0.001 g cell dry weight/l). Finally, mannitol isolation under optimum fermentation conditions was achieved. The mannitol production obtained in this study is the highest reported so far by a wild-type L. reuteri strain and, more interestingly, using a simplified culture medium.

Global Analysis of Mannitol 2-Dehydrogenase in Lactobacillus reuteri CRL 1101 during Mannitol Production through Enzymatic, Genetic and Proteomic Approaches

“…The highest activity values (3.646 U/mg protein) were found during early microbial growth phases (log phase), independently of the assayed culture conditions [14]. Additionally, when the strain was grown at constant pH in a range between 6.0 and 4.8, no significant differences in the obtained MDH activity values were observed [15]. Here, the enzyme activity values of L .…”

“…Enzymatic activity was determined according to the method described previously [15]. Briefly, protein extracts were diluted to obtain a protein concentration of 0.5 mg prot/mL.…”

“…In previous work we demonstrated that the heterofermentative strain Lactobacillus reuteri CRL 1101 efficiently produced mannitol in both rich and simplified culture media containing sugarcane molasses as carbon source [14,15]. Maximum mannitol concentrations (38 and 41.5 g/L) and yields (Y Mtl: 86.9 and 105%) were attained using 7.5% (w/v) of sugar from sugarcane molasses when grown in agitated cultures at 37°C under free- and constant (5.0)-pH conditions, respectively, after 24 h of incubation.…”

13C mannitol as a novel biomarker for measurement of intestinal permeability

“…The excretion of 13 C mannitol drops between 8-24 hours, however the 12 C mannitol excretion continues to peak in that time frame. This could be possibly due to inadvertent contamination during the study (either from dietary, medications or other sources), baseline sugar competing with absorption or due to production of 12 C mannitol by colonic microbiota during the testing (11). Figure 1 (panel B) shows a representative tracing from a urine sample showing the lower baseline and 8-24 hour excretion of 13 C mannitol.…”

Constipation-Predominant Irritable Bowel Syndrome Females Have Normal Colonic Barrier and Secretory Function

“…However, there is significant inter-day variability in excretion of those sugars [23] and about a third of the subjects excrete significant amounts of mannitol at baseline [12]. This could be due to inadvertent contamination during the study (either from diet, medications or other sources), baseline sugar competing with absorption or the production of 12 C mannitol by colonic microbiota during the testing [24]. 13 C constitutes only 1% of naturally occurring carbon and is a stable (non-radioactive) isotope.…”