Energy & redox fluxes in Lactobacillus reuteri DSM 17938 on different sugars

Abstract

Under anaerobic condition the specific growth rate of Lactobacillus reuteri DSM 17938 on different sugars, was analyzed using spectrophotometry. Electron acceptor (fructose) supported cells to cope with poor energy recovery by re-oxidising the NADH, thus enabling ATP formation thru acetate production, while fermenting glucose via the phosphoketolase pathway (PKP) and simultaneously operating via Embden-Meyerhof pathway (EMP). The specific growth rate on glucose, maltose and sucrose was improved unquestionably in the presence of fructose.

Analysis of the fermentation products showed in the fermentations without fructose produced relatively more ethanol than in all other cases studied so far with L. reuteri DSM 17938. It indicated that the enzyme pyruvate dehydrogenase (PDH) is active. It can be hypothesized that the particular growth environment (SD4 without electron acceptor) caused intracellular conditions that activated PDH. Comparison with the literature revealed that this enzyme is highly regulated on metabolic level by a number of metabolites.

In short, this study displayed that the environmental conditions (anaerobic, pH 5.5) together with medium composition (SD4) had an effect of the fluxes through the two central carbon pathways in L. reuteri DSM 17938, which had no apparent effect on the energy and redox fluxes. Due to that ethanol could be produced via each pathway it made it impossible to estimate the flux in each pathway. Therefore, two extreme cases, regarding the variation in the cofactor formation flux ratio, RJ (ratio between the redox formation flux (JNADH+NADPH), and the energy carrier formation flux (JATP)), were investigated: PDH not active (SD4 media with e- acceptor) and PDH active (SD4 media without e- acceptor). The real case is somewhere between the two cases. Thus the results need verification and further experiments.
Additionally the data obtained from osmotic potential measurements reflected the product formed during the fermentation and showed linear correlation between osmotic potential and optical density.

Popular Abstract

L.reuteri DSM 17938 is a bacterium isolated from breast milk and it is known being beneficial for the human gut. In the commercial production the bacterium is grown in the fermentation tank and than used in tablets. The knowledge of the bacterium behavior is a key for a good growth and subsequently good product.

Sugar, medium composition and oxygen are impotent components for the bacterial growth. Sugar is the carbon source and oxygen is needed to gain energy. This study investigates changes in the metabolic pathways of L.reuteri when grown on different sugars and specific medium. Sugars such as glucose, maltose and sucrose are used and also combined with fructose. As we grow the bacteria in the tank without oxygen the fructose helps the bacterium obtain energy, fructose is en electron acceptor.

Using the spectrophotometer measurements we can estimate bacterial growth, how much and how fast our organism grow. Using the chromatography we can identify and calculate amount of the product produced by L. reuteri. Amount of products such as acetate, ethanol and lactate. Results from these two methods, growth velocity and amount of product produced, allow to predict the metabolic pathways taken by bacterium. Usually two pathways can be taken: one producing just lactate (homofermentation) and the other producing acetate and ethanol (heterofermentation).

Results from these study show that the environmental conditions together with medium composition had an effect on product produced thus the metabolic pathways taken by L. reuteri. Analysis of the fermentation products showed in the fermentations without fructose produced relatively more ethanol than in all other cases studied so far with L. reuteri DSM 17938. It indicated that the enzyme pyruvate dehydrogenase (PDH) is active. It can be hypothesized that the new metabolic pathway was taken connecting homo and heterofermentative pathways.
Particular growth environment (medium without electron acceptor) caused intracellular conditions that activated PDH. Comparison with the literature revealed that this enzyme is highly regulated on metabolic level by a number of metabolites.

• author: Bengtsson, Katarzyna
• supervisor: Ed van Niel
• organization: Applied Microbiology; Biotechnology
• course: KMBM01 20191
• year: 2019
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences; Chemistry; Technology and Engineering
• keywords: Energy, redox fluxes, Lactobacillus reuteri DSM 17938, different sugars, applied microbiology, teknisk mikrobiologi
• language: English
• id: 8987542
• date added to LUP: 2019-07-04 14:40:47
• date last changed: 2019-07-04 14:40:47