# Presentation: 493381

##     Pyruvate Metabolism of Desulfovibrio desulfuricans strain G20 

**and a Cytochrome *****c******3****** *****Mutant**
**Barbara J. Giles, Kate E. Hart, Judy D. Wall **
**Department of Biochemistry, University of Missouri-Columbia**

**HPLC Analysis of **
**Culture Filtrates**

**WT and ****CycA****-**** Mutant**** ****Growth on Pyruvate Sulfate**

**WT and ****CycA****-**** ****Mutant**** ****Fermentative Growth on Pyruvate**

**Comparison  of WT and CycA****-**** Mutant Growth on **
**Pyruvate and  Pyruvate Sulfate**

**WT and ****CycA****-**** Mutant**** ****Growth on Lactate Sulfate**

**This research was funded through the Department of Energy.**

**The versatility of SRB energy generating processes makes the many environmental impacts of these bacteria possible. A “hydrogen-cycling” model was proposed over twenty years ago to explain how these bacteria may augment energy generation during respiration.  Cytochrome *****c*****3**** (type 1 tetraheme cytochrome *****c*****3****) is a key to the proposed route of electron flow.  A mutant of *****Desulfovibrio desulfuricans *****G20 that lacks functional cyt *****c*****3**** produces a significant portion of the reductant generated from lactate oxidation as hydrogen.  The absence of cyt *****c*****3**** apparently blocks re-oxidation of that hydrogen.  The lack of cyt *****c*****3**** eliminates respiration of sulfate with pyruvate as electron acceptor, restricting growth on pyruvate to fermentation.  Neither sulfate nor fumarate is used as a terminal electron acceptor when this tetraheme cytochrome is absent.  These data support a “hydrogen-cycling” model for respiration of pyruvate with sulfate; however, the hydrogen atoms may be carried by formate, a possibility yet to be explored.**

**Possible pathways for electrons generated by pyruvate fermentation are indicated by “dashed” lines.  The green box covers those routes which are impaired when there is no functional cytochrome *****c*****3. ****PFOR Pyruvate Ferredoxin Oxidoreductase; QMO Quinone-interacting Membrane-bound Oxidoreductase**; **HMC High Molecular weight Cytochrome; Dsr Dissimilatory Sulfite Reductase**

**Abstract**

**Pyruvate**

**Acetate**

**Fumarate**

**Succinate**

**Formate**

**Lactate**

**Formate**

**Pyruvate**

**Acetate**

**Succinate**

**An Aminex HPX-87H HPLC column was used to separate, identify and quantitate the organic compounds present in filtrates of fermentatively grown cultures.  5 mM H****2****SO****4**** was the mobile phase.  **

- Minutes

**Cytochrome *****c*****3**** is a requirement for respiration of pyruvate with sulfate as the electron acceptor.  In the absence of *****c*****3****, only pyruvate fermentation is possible. **
**2. Cells lacking cytochrome *****c*****3 ****can still respire with electrons from lactate. **
**3. Delivery of electrons to internal cytoplasmic electron acceptors, such as sulfate or organic acids, is dependent upon the presence of cytochrome *****c*****3****. This is seen by the generation of significant amounts of succinate during pyruvate fermentation by WT as compared to the CycA****-**** mutant.**

**Conclusions**

**Notes:**
I2 lactate, sulfate, CO2, carbon accting?, yen 36 ->1/2 growth for I2 (can’t use pyruvate)
Promoter, western