Optimization of Cultivation Conditions for the Lactobacillus reuteri LR1 Strain to Improve the Biosynthesis of Bacteriocin-Like Substances

Abstract

The article presents the results of optimization of the culturing conditions to increase the production of bacteriocin-like compounds (presumably including reuterin) by the Lactobacillus reuteri strain LR1. The strain Escherichia coli ATCC 25922, an opportunistic microorganism, the content of which is standardized in foods by the Food Safety Legislation, was selected as an indicator strain of antimicrobial activity. The nutrient medium for L. reuteri LR1 cultivation was optimized to increase the production of bacteriocin-like compounds, and the parameters of two-stage growth of the producer were established: (1) cultivation on the initial medium for biomass accumulation and (2) growth on a water–glycerol medium to convert glycerol to antimicrobial compounds, presumably reuterin. The first stage was carried out as follows: the L. reuteri LR1 culture (5%) was inoculated into a medium with the following composition: hydrolyzed milk—250 mL/L; yeast extract—10 g/L; peptone—5 g/L; glucose—20 g/L; sodium acetate—5.0 g/L; monosubstituted potassium phosphate—2.0 g/L; magnesium sulfate—0.2 g/L, and manganese sulfate—0.5 g/L, pH 6.4–6.6. The cultivation was carried out for 18 h at (37 ± 1)°С. The second stage included the incubation of the obtained biomass in 200 mM of glycerol-containing aqueous solution, pH 6.6, for 2 h at 37°С. The zone of E. coli inhibition caused by the produced bacteriocin-like compounds was 25 mm.