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.

Popular Abstract

The response to how an oxygen-sensitive bacterium is able to thrive in environments with high oxygen concentrations

Probiotics are living microorganisms that could induce health benefits to the host as the improvement of nutrients bioavailability or the treatment of different intestinal disorders (e.g. constipation, diarrhea) when they are consumed in adequate amounts. Considering these potential health beneficial effects, probiotics have been increasingly incorporated during the last two decades to several supplements and food products. Among the different probiotics on the market, Lactobacillus reuteri strain DSM 17938 is a probiotic bacterium that is able to tolerate high oxygen concentrations compared with other probiotic bacteria. This distinctive feature represents an advantage on the production and storage of L. reuteri DSM 17938, as in general, probiotic manufacturers face difficulties in preserving the viability of probiotics in their final matrix (e.g. food products) as most of the probiotics cannot resist oxygen (strict anaerobes) or only tolerate it at low concentrations. However, it is not clear what mechanisms allows this bacterium to thrive and resist high concentrations of oxygen in comparison with other strains, even of the same species. Therefore, the main objective of this study was to elucidate the chemical transformations catalyzed by enzymes inside the probiotic (enzymatic mechanisms) which allows it to tolerate high concentrations of oxygen and their effect in the metabolism.

The production of the probiotic at four oxygen concentrations (0%, 7%, 14% and 21% of oxygen) showed that the strain was able to tolerate these conditions, as there was not hydrogen peroxide production (H2O2), a harmful molecule for the organism, under none of the conditions evaluated. In contrast, most of the probiotic strains produce high concentrations of this molecule at low concentrations of oxygen, which inhibits their growth. Moreover, the investigation found that the increase of the oxygen concentration on the media increased the production of the enzymes NAD(P)H oxidases, NAD(P)H peroxidases, and glutathione peroxidase in a proportional way with respect to the oxygen concentration. These results indicate that the lack of hydrogen peroxide production is due to, at least in part, the action of the identified enzymes. On the other hand, the analysis of the metabolic end-products showed a reduction in the concentrations of ethanol and lactate produced by the probiotic, at high oxygen levels, while the concentration of acetate increased. These findings are remarkably important, as other investigations has found this change as a clear indicator that the strain is utilizing oxygen in its metabolism. In conclusion, the findings of this study indicate the system composed by the enzymes NAD(P)H oxidase, NAD(P)H peroxidase and glutathione peroxidase is the main mechanism used by the strain L. reuteri DSM 17938 to tolerate and thrive in the presence of high concentrations of oxygen.

• author: Rivera Ramirez, Julian David
• supervisor: Christer Larsson
• organization: Applied Microbiology; Biotechnology
• course: KMBM01 20191
• year: 2019
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences; Chemistry
• keywords: Applied microbiology, Teknisk mikrobiologi
• language: English
• id: 8992586
• date added to LUP: 2019-09-12 10:30:14
• date last changed: 2020-12-24 03:40:28