Oxygen Metabolism in Lactobacillus reuteri. DSM 17938 and PTA 4659

Abstract

A previous study found that oxygen can promote the growth of Lactobacillus reuteri DSM 17938 and PTA 4659 (Koendjbiharie, 2015). However, the presence of oxygen is a cause of H2O2 accumulation, which can result in impaired growth. The first part of this project was to investigate survivability of cells when treated with H2O2. The results revealed that the higher the concentration of H2O2, the lower the growth rate of L. reuteri became. Moreover, L. reuteri PTA 4659 can endure H2O2 up to 400 M before it starts to become inactive or die, whereas L. reuteri DSM 17938 can tolerate H2O2 up to 800 M. A study of the relation between production of H2O2 and dissolved oxygen tension (DOT) was also conducted. For strain DSM 17938 it was found that the DOT needs to reach a critical level of around 55 – 65%, before cells produce H2O2 and when the oxygen present in the system is almost utilised by the cells, water will be formed instead. The formation of H2O2 is delayed, which means H2O2 generates after the oxygen was presented in the medium and once the dissolved oxygen decreased, the production of H2O2 was still continued after which it declined to zero. However, what will happen if cells are given oxygen at a constant DOT is still unclear. According to the results that were obtained, it seems that cells number were increasing as there were more, but smaller, cells in aerated cultures. To confirm this, more experiments need to be done.

Popular Abstract

At first glance, it seems to be abstract when seeing this topic that composed of fancy words. Let’s make it more approachable by separated the heading into two terms. First, ‘L. reuteri DSM 17938 and PTA 4659’, which refer to consumable ‘good bacteria’. The reason why it is called ‘good bacteria’ is because this type of bacteria provides a lot of health benefits, such as preventing the risk of diarrhea. One interesting point of these bacteria is that they can grow in both the presence and absence of oxygen and from this point, it is related to the second term which is ‘metabolism’. Metabolism is a series of controlled chemical reactions that convert a substrate into products for the purpose of maintaining cells activity, i.e., energy production. As aforementioned, L. reuteri can grow when there is oxygen present in the system. So oxygen metabolism of L. reuteri DSM 17938 and PTA 4659 is the study about what is going on when cells are growing in the presence of oxygen.

In a previous study it was found that L. reuteri has a better growth under the condition where oxygen was introduced since more energy was produced. However, the presence of oxygen is a cause of hydrogen peroxide formation, which can result in restricted growth. From this it leads to the first part of the experiment, to investigate what will happen if cells are growing in medium with different hydrogen peroxide concentrations (0 – 1000 mM). The result revealed that the higher the hydrogen peroxide concentration, the slower the growth became. Moreover, L. reuteri PTA 4659 could endure hydrogen peroxide up to 400 mM before it started to become inactive or die, whereas L. reuteri DSM 17938 could tolerate hydrogen peroxide up to 800 mM.

Since the production of hydrogen peroxide is related to oxygen, second part of this study was conducted to find the relation between the formation of hydrogen peroxide and oxygen. The experiments were divided into two parts.
(1) Cells were grown in batch mode. It was found that the formation of hydrogen peroxide was formed after there was clearly a high dissolved oxygen concentration, meaning that there was a kind of delay in the generation of hydrogen peroxide. Once the dissolved oxygen concentration decreased, hydrogen peroxide was still produced after which its concentration slowly declined to zero. Besides, it was also found that it was not possible with the system to create a constant dissolved oxygen concentration because there was a constant increase of cells and thus an increasing demand of oxygen consumption, but without any formation of hydrogen peroxide.
(2) Cells of strain DSM 17938 were grown in such a way that it was possible to set a constant dissolved oxygen concentration in the culture to study the behaviour of the cells. To do this, it was necessary to set the conditions such that the cells grow at one growth rate, which can be done in a continuous culture mode. Hereby fresh medium is pumped in, and simultaneously the same amount of volume culture is pumped out per time to keep the working volume in the reactor constant. However, the outcome was contradicted to expectation, cells were managing to take up the oxygen in the medium. One possible assumption would be cells number were rose, as there were more cells in high aerated cultures than under anaerobic conditions. In addition, it has been observed that the formation of hydrogen peroxide might be a function of the oxygen concentration in the medium which mean it might need to reach ‘a value’ before hydrogen peroxide started to generate.
According to all results that were obtained, it remains unclear what will happen if cells are given oxygen at a certain dissolved oxygen concentration. It appears as if DSM 17938 had a capacity to adapt to increasing aeration regimes. Therefore, further studies are needed to be done.

• author: Artsanchorn, Pimprakay
• supervisor: Christer Larsson
• organization: Applied Microbiology; Biotechnology
• course: KMBM01 20181
• year: 2018
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences; Technology and Engineering
• keywords: applied microbiology, teknisk mikrobiologi
• language: English
• id: 8945555
• date added to LUP: 2018-06-18 15:39:15
• date last changed: 2018-06-18 15:39:15