Using microorganisms culture supernatants to supply enzymes to biofuel cells and extend cathode lifetime

Hochschulschrift

Zusammenfassung: Biofuel cells show great potential for the environment-friendly direct conversion of chemically stored energy into electricity. Microbial fuel cells use microorganisms and enzymatic fuel cells use purified enzymes as electro-catalysts. This omits the need to supply expensive noble metal catalysts. Microbial fuel cells typically have longer lifetimes than enzymatic fuel cells because microorganisms are able to regenerate, while enzymes usually degrade or become inactivated more quickly. The enzyme purification procedure is also time consuming and costly. However, higher current densities can typically be achieved with enzymatic fuel cells. The aim of the work described in this thesis was to combine the advantages of microbial (typically longer lifetimes) and enzymatic (typically higher current densities) fuel cells.Results described in this thesis show, for the first time, that supernatants of different enzyme-secreting microorganisms such as yeast, fungi and bacteria can be used to supply unpurified enzymes to the electrodes of biofuel cells without the addition of mediators. This obviates the need for elaborate and expensive enzyme purification, and simplifies the construction process. Furthermore, this thesis shows a first demonstration that with regular re-supply of fresh enzyme-containing culture supernatant, the lifetime of an enzymatic electrode can be extended. Therefore, the construction of a self-regenerating biofuel cell in which enzyme-secreting microorganisms continuously supply catalysts at the electrode could be feasible.At the cathode, laccase-containing supernatant (3.4 U mL-1 laccase, pH 5) of the fungus T. versicolor yielded the best cathode performance with current densities of 129 ± 19 µA cm-2 at 0.644 V vs. NHE. The achieved current density was even slightly higher than the current density recorded for cathodes supplied with purified laccase of the same activity. With laccase-containing supernatant (0.06 U mL-1 laccase, pH5) from the recombinant yeast Y. lipolytica YL4, a current density of 6.7 ± 0.4 μA cm−2 at 0.644 V vs. NHE was achieved. The use of a copper efflux oxidase (CueO)-containing supernatant (0.034 * 10-1 U mL-1 CueO, pH 5) of E.coliCueO resulted in a high current density of 119 ± 23 μA cm−2 , similar to the results achieved with supernatant of T. versicolor, but at a lower potential of 0.400 V vs. NHE, due to the lower redox potential of CueO. In contrast to laccase-containing supernatant, CueO-containing supernatant was also electro-catalytic active at pH 7.4 but at a 0.250 V lower potential at a current density of 100 µA cm-2 compared to its use at pH 5. At the anode, cellobiose dehydrogenase (CDH)-containing supernatant (0.08 U mL-1 CDH, pH 5) from the recombinant yeast Y. lipolytica YPC4 resulted in the highest current density of 39.1 ± 5.9 µA cm-2 at 0.600 V vs. NHE. A current density of 27.6 ± 1.3 µA cm-2 at 0.600 V vs. NHE, was achieved with supernatant of the fungus P. chrysosporium (0.12 U mL-1 CDH, pH 5).Also, complete biofuel cells solely supplied with microorganism culture supernatant were constructed and resulted in a maximum power density of 6.2 ± 1.2 µW cm-2 with laccase-containing supernatant from the fungus T. versicolor at the cathode and CDH-containing supernatant of the yeast Y. lipolytica YPC4 at the anode. The achieved power density was reduced by only around 50% compared to the use of purified enzymes, and was even in the same range as was reported for biofuel cells using purified laccase and CDH. Biofuel cells based on complete fungi (T. versicolor, laccase and P. chrysosporium, CDH) and complete yeast (Y. lipolytica YL4, laccase and Y. lipolytica YPC4, CDH) supernatants resulted in maximum power densities of about 5 µW cm-2 and 1 µW cm-2, respectively. Higher enzyme activity did not always lead to higher current densities. Components in the cultivation medium or secreted byproducts can reduce the electrode performance. Therefore, the possibility to use different microorganisms opens more options for their application at biofuel cells. The use of fungal supernatants is attractive for applications outside the laboratory where the use of genetically modified organism such as Y. lipolytica YL4 and YPC4 and E.coliCueO can be highly regulated. However, a continuous enzyme production might more easily be obtained with unicellular, planktonic yeast and bacteria.Finally, it was demonstrated that the lifetime of a cathode can be extended by at least 5-fold up to 120 days with the re-supply of fresh laccase-containing supernatant of T. versicolor at a continuous galvanostatic load of 50 µA cm-2. During the operation time, no gradual decay was recorded and the experiment had to be stopped due to technical reasons. Therefore, it is very likely that a longer lifetime is possible.Future work could concentrate on the construction of self-regenerating biofuel cells in which enzymes are supplied continuously at the electrodes by microorganisms. In this respect, it would be interesting to test if a lifetime extension is also possible by re-supplying enzyme containing supernatant of Y.lipolytica YL4 and YPC4, E. coliCueO or P. chrysosporium. Furthermore, the application of supernatants with increased enzyme activity could increase the achieved current density. Future work could also include the screening of alternative supernatants containing other enzymes such as bilirubin oxidase, which is electro-catalytically active at neutral pH. The combination of cathodes based on culture supernatant with a microbial anode would also be very interesting to investigate, because microbial anodes exhibit high current densities and have long lifetimes, but the cathode often limits the performance of complete microbial fuel cells

Angaben zum Objekt

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: Albert-Ludwigs-Universität Freiburg, Dissertation, 2015

Klassifikation und Themen

• Klassifikation: Biowissenschaften, Biologie
• Schlagwort: Laccase ; Cellobiose-Dehydrogenase ; Schmetterlingsporling ; Phanerochaete chrysosporium ; Yarrowia lipolytica ; Escherichia coli

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2016
• Urheber: Sané, Sabine
• Beteiligte Personen und Organisationen: Zengerle, Roland

Weitere Informationen

• DOI: 10.6094/UNIFR/10502
• URN: urn:nbn:de:bsz:25-freidok-105024
• Rechteinformation: Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 25.03.2025, 13:51 MEZ