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Limosilactobacillus reuteri is a probiotic microorganism used in the treatment of gastrointestinal disorders. The effect of oxygen transfer on cultures of L. reuteri ATCC 53608 at shake flask and stirred tank bioreactor scales was studied, using MRS and molasses-based media. At shake flask scale, in MRS medium, a maximum bacterial concentration of 2.01 ± 0.02 g L−1 was obtained; the oxygen transfer coefficient was 2.01 ± 0.04 h−1. Similarly, in a 7.5 L bioreactor, in MRS, a maximum bacterial concentration of 2.46 ± 0.16 g L−1 was achieved (kLa = 2.64 ± 0.06 h−1). In contrast, using a molasses-based medium, bacterial concentration reached 3.13 ± 0.17 g L−1 in the 7.5 L bioreactor. A progressive reduction in lactic acid concentration and yield was observed as the oxygen transfer coefficient increased, at shake flask scale. Also, the oxygen transfer coefficient strongly affected the growth of L. reuteri in shake flask and bioreactor and allowed us to successfully scale up L. reuteri culture, producing similar maximum bacterial concentrations in both scales (2.01 g L−1 and 2.46 g L−1 in MRS). This is the first study on oxygen transfer coefficients in L. reuteri, and it is a valuable contribution to the field as it provides important insights about how this organism tolerates oxygen and adapts its metabolism for larger biomass production. [ABSTRACT FROM AUTHOR]