Physiological adaptive mechanism to oxidative stress in Lactobacillus reuteri DSM 17938

Abstract: Probiotics are living microorganisms which could induce a potential health benefit to the host when consumed in adequate amounts. Among the different probiotics in the market, Lactobacillus reuteri strain DSM 17938 is a microaerophilic and heterofermentative organism that is able to tolerate high oxygen conditions compared with another L. reuteri and lactic acid bacteria strains. This study investigated the enzymatic and metabolic responses to oxidative stress by L. reuteri DSM 17938 and its effects on the enzymatic activities, the metabolism and survivability of the cells. Cultivation under aerobic conditions at different levels of aeration, 0%, 33%, 66% and 100% of air at 0.5 L/L/min, did not trigger a significant increase on the concentration of hydrogen peroxide (H2O2) accumulated that could affect generating an inhibitory effect. Specific enzymes activities were evaluated for NAD(P)H oxidases, NAD(P)H peroxidases and glutathione peroxidase; characteristic enzymes associated with the enzymatic oxidative stress mechanisms. A ten to thirty-fold increase in the activity of the NAD(P)H oxidases, NAD(P)H peroxidases, and glutathione peroxidase, proportional on the level of oxygen supplied to the system after a threshold of 33% of air at a rate of 0.5 L/L/min. The enzyme assays suggest that the lack of accumulation of H2O2 in the media was absorbed by the NAD(P)H peroxidases and glutathione peroxidase which were constitutively-active under anaerobic conditions but with a higher induction at higher aeration rates in contrast to NAD(P)H oxidase. The different levels of aeration were sufficient for a significant reduction in end-products typically found during anaerobic growth, ethanol and lactate, and an increase of the concentration acetate. At different levels of oxygen, NAD(P)H is mainly regenerated by the NA(P)DH oxidase - peroxidases system rather than through the production of ethanol and lactate allowing L. reuteri to produce an extra ATP by the production of acetate. These observations indicated that a coupled NAD(P)H oxidase – NAD(P)H peroxidase – glutathione peroxidase system was the main oxidative stress resistance mechanism in L. reuteri DSM 17938, and was regulated by oxygen availability.