Becky L. Treu

Isolation and purification of PQQ-dependent lactate dehydrogenase from Gluconobacter and use for direct electron transfer at carbon and gold electrodes

This research details the isolation and purification of a new type of lactate dehydrogenase that is dependent upon the coenzyme pyrroloquinoline quinone (PQQ). PQQ-dependent enzymes have been of interest in the literature over the last decade due to the fact that many of them can undergo direct electron transfer (DET) at electrode surfaces which is of interest for biosensor and biofuel cell applications. In the paper, we detail the isolation of PQQ-dependent lactate dehydrogenase (PQQ-LDH) from two sources of Gluconobacter (Gluconobacter sp. 33 and Gluconobacter suboxydans). This paper also shows the first evidence that PQQ-LDH can undergo direct electron transfer at gold and carbon electrode surfaces for future use in biosensors and biofuel cells.

Ability of a haloalkaliphilic bacterium isolated from Soap Lake, Washington to generate electricity at pH 11.0 and 7% salinity

A variety of anaerobic bacteria have been shown to transfer electrons obtained from organic compound oxidation to the surface of electrodes in microbial fuel cells (MFCs) to produce current. Initial enrichments for iron (III) reducing bacteria were set up with sediments from the haloalkaline environment of Soap Lake, Washington, in batch cultures and subsequent transfers resulted in a culture that grew optimally at 7.0% salinity and pH 11.0. The culture was used to inoculate the anode chamber of a MFC with formate as the electron source. Current densities up to 12.5 mA/m2 were achieved by this bacterium. Cyclic voltammetry experiments demonstrated that an electron mediator, methylene blue, was required to transfer electrons to the anode. Scanning electron microscopic imaging of the electrode surface did not reveal heavy colonization of bacteria, providing evidence that the bacterium may be using an indirect mode of electron transfer to generate current. Molecular characterization of the 16S rRNA gene and restriction fragment length profiles (RFLP) analysis showed that the MFC enriched for a single bacterial species with a 99% similarity to the 16S rRNA gene of Halanaerobium hydrogeniformans. Though modest, electricity production was achieved by a haloalkaliphilic bacterium at pH 11.0 and 7.0% salinity.

Bioelectrocatalysis of Pyruvate with PQQ-dependent Pyruvate Dehydrogenase

Although pyruvate has not been considered as a fuel for an enzymatic biofuel cell, there are dehydrogenase enzyme capable of oxidizing pyruvate. This paper details the discovery of a pyrroloquinoline quinone-dependent pyruvate dehydrogenase (PQQ-PDH) in Gluconobacter species. A method was developed to isolate and purify PQQ-PDH from Gluconobacter, along with the characterization of the purified enzyme. It was found that the purified enzyme can undergo direct electron transfer at carbon electrodes surfaces, which allowed for its incorporation into a pyruvate biofuel cell. It was also found that PQQ-PDH lacks substrate specificity, which minimizes its usefulness in many sensor applications, but is advantageous for deep oxidation in biofuel cell anodes.

Enzymatic Biofuel Cells

Publisher Summary This chapter examines the development of enzymatic biofuel cells over the last four decades. Like traditional PEM fuel cells, biofuel cells consist of an anode and cathode separated by a membrane. The difference is that biofuel cells eliminate the dependence on precious metal catalysts by replacing them with biological catalysts. Biofuel cells can be categorized as microbial fuel cells and/or enzymatic biofuel cells. Microbial fuel cells utilize living microorganisms to oxidize the fuel, whereas enzymatic fuel cells employ isolated enzymes. A comparison of enzymatic biofuel cells to traditional fuel cells is presented and the types of enzymes employed at the anode and cathode of biofuel cells, along with strategies for immobilization of those enzymes at electrode surfaces are discussed. A detailed comparison of mediated electron transfer and direct electron transfer, along with discussion of the advantages and disadvantages of both types of electron transfer mechanisms are also discussed in the chapter. Furthermore, the chapter describes the importance of metabolic pathways in enzymatic biofuel cell development and fuel cell design and engineering issues for enzymatic biofuel cells.