1. Rabeay Hassan and Ursula Bilitewski
Simple Electrode System for the Detection of Viable Candida albicans and Investigations of Respiratory Pathways
Rabeay Hassan and Ursula Bilitewski
Helmholtz Centre for Infection Research
„Direct communication between living yeasts and electrodes“ as original title
DGHM Jahrestagung Göttingen

2. Objectives
Utilisation of electrochemical methods for the detection of viable yeasts, in particular Candida albicans
Optimisation of the experimental set-up to be able to exploit the bioelectrochemical properties of C. albicans for diagnostic purposes
Proposal of electrochemical methods as a tool for studies of the structure and function of mitochondria
Electrode System for the Detection of Yeasts

3. Experimental approach: Voltammetry
Three-electrode setup: (1) Carbon Paste working electrode;
(2) Platinum auxiliary electrode;
(3) Ag/AgCl reference electrode
Variation of current with the potential due to electron transfer
Electrode System for the Detection of Yeasts

4. Electrochemical oxidation of yeast species
C. albicans
S. cerevisiae
Dead cells
Electrochemical conditions
Supporting electrolyte is phthalate buffer, pH 7, scan rate is 50 mV/s.
C. albicans, S. cerevisiae and dead cells of C. albicans at cell concentrations of 3.8x10^6, 9.15x10^6 and 2.2x10^6 /ml, respectively.
Voltammetric behavior of living cells of C. albicans and S.cerevisiae
Electrode System for the Detection of Yeasts

5. Correlation to cell numbers of C. albicans
Electrode System for the Detection of Yeasts

6. Bioelectrochemical Mechanism: Influences of Carbon Sources
The increased signal from S. cerevisiae which were cultivated with the non-fermentable carbon source galactose points to the respiratory chain as electron source.
Electrode System for the Detection of Yeasts

7. Scheme of the C. albicans respiratory chain
SHA
Antimycin
KCN
Rotenone
J Bioenerg Biomembr (2006) 38:129–135
Electrode System for the Detection of Yeasts

8. Influences of Respiratory Chain Inhibitors
Rotenone: complex I; Antimycin: complex III; KCN: complex IV (COX)
Electrode System for the Detection of Yeasts

9. Inhibition of the alternative oxidase (AOX)
SHA; Salicylhydroxamic acid
Electrode System for the Detection of Yeasts

10. Oxidation Current
SHA
Antimycin
KCN
Rotenone e-

11. Electron transfer steps in cytochrome c oxidase
matrix
Electrode System for the Detection of Yeasts

12. Deletion of genes for subunits of cytochrome c oxidase
Single gene deletion mutants of S. cerevisiae deliver lower electrochemical signals, which correlate with lower oxygen consumption rates.
Electrode System for the Detection of Yeasts

13. Conclusion C. albicans can directly transfer electrons to electrodes
Electrochemical signals increase with the number of viable cells and can be used for diagnosis purposes
The signal originates from the activity of cytochrome c oxidase (COX)
Electrochemical systems can be used for screening of new drugs affecting the electron transport chain (ETC)
Electrode System for the Detection of Yeasts

14. Helmholtz Centre for Infection Research
ACKNOWLEDGEMENT
Egyptian ministry of higher education and scientific research, and National Research Centre NRC, Cairo- Egypt
Helmholtz Centre for Infection Research
Electrode System for the Detection of Yeasts

15. Group members 2009

16. Thanks for your attention
Rabeay Hassan

18. Focus on Issues How to obtain electricity from microorganisms?
Where does electricity come from?
Which microorganisms and what is the essential aim of this work?