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The influence of electrochemically generated hydrogen peroxide on the stress response of microorganisms for the purpose of increased PHA production
Najbrtová, Johana ; Nováčková, Ivana (referee) ; Ehlich, Jiří (advisor)
The subject of the presented thesis is the effect of electrochemically formed hydrogen peroxide on the production of polyhydroxyalkanoate. In this work, hydrogen peroxide was generated directly in the medium with bacteria by two-electron reduction of oxygen. This thesis is divided into a theoretical part, which is devoted to approaching the topic of polyhydroxyalkanoate, oxidative stress, electrochemical production of H2O2 and the connection of electrochemistry with biotechnology. The experimental part is focused on the application of these findings. Hydrogen peroxide was generated by applying an electrical potential to an electrode system composed of a stainless-steel working electrode, a titanium counter electrode, and a pseudo-reference Ag/AgCl electrode embedded in a polypropylene holder. After initial electrochemical characterization of the prepared system, a potential of 0,8 V and -1 V was selected for application in cultivation experiments. Here, the effect of H2O2 on the stress response of the bacterium Cupriavidus necator H16 from the Czech collection of microorganisms was investigated. From the results of the cultivation experiments, it was evident that the electrochemically produced H2O2 does not have a significant effect on the development of the bacterial culture. However, the electrode system itself positively affects bacterial growth. The influence of H2O2 was not noticeable due to the low production in medium. This was caused by a low concentration of oxygen in the medium. During this work, a new electrode system with higher H2O2 production was designed, which could use atmospheric oxygen for reduction to H2O2. However, even with this system, a desired stress response was not achieved, because increased production of H2O2 was prevented by the formation of biofilm on the electrodes. Furthermore, it was found that the materials used for the electrode system support the formation of biofilm, mainly titanium, stainless-steel mesh and polypropylene.
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