4.6 Article

Non-inhibitory levels of oxygen during cultivation increase freeze-drying stress tolerance in Limosilactobacillus reuteri DSM 17938

Journal

FRONTIERS IN MICROBIOLOGY
Volume 14, Issue -, Pages -

Publisher

FRONTIERS MEDIA SA
DOI: 10.3389/fmicb.2023.1152389

Keywords

online flow cytometry; k mean clustering; fatty acid; bile and acid tolerance; 5 ' nucleotidase; Limosilactobacillus reuteri DSM 17938; oxygen; freeze-drying

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The study investigated the effects of oxygen on Limosilactobacillus reuteri DSM 17938 during cultivation and the resulting properties of the freeze-dried probiotic product. It was found that low levels of oxygen did not influence the growth kinetics of the bacterium, but did affect the redox metabolism and production of acetate and ethanol. Cells cultivated in the presence of oxygen showed higher survival rates, increased unsaturated fatty acid content, improved bile tolerance, and higher 5' nucleotidase activity. However, they exhibited lower tolerance to acidic conditions compared to bacteria grown under complete anaerobic conditions. Overall, controlled oxygen supply during production can optimize the probiotic activity of L. reuteri DSM 17938.
The physiological effects of oxygen on Limosilactobacillus reuteri DSM 17938 during cultivation and the ensuing properties of the freeze-dried probiotic product was investigated. On-line flow cytometry and k-means clustering gating was used to follow growth and viability in real time during cultivation. The bacterium tolerated aeration at 500mL/min, with a growth rate of 0.74 +/- 0.13h(-1) which demonstrated that low levels of oxygen did not influence the growth kinetics of the bacterium. Modulation of the redox metabolism was, however, seen already at non-inhibitory oxygen levels by 1.5-fold higher production of acetate and 1.5-fold lower ethanol production. A significantly higher survival rate in the freeze-dried product was observed for cells cultivated in presence of oxygen compared to absence of oxygen (61.8%+/- 2.4% vs. 11.5%+/- 4.3%), coinciding with a higher degree of unsaturated fatty acids (UFA:SFA ratio of 10 for air sparged vs. 3.59 for N-2 sparged conditions.). Oxygen also resulted in improved bile tolerance and boosted 5 ' nucleotidase activity (370U/L vs. 240U/L in N-2 sparged conditions) but lower tolerance to acidic conditions compared bacteria grown under complete anaerobic conditions which survived up to 90min of exposure at pH 2. Overall, our results indicate the controlled supply of oxygen during production may be used as means for probiotic activity optimization of L. reuteri DSM 17938.

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