Cytochrome c(3) mutants of Desulfovibrio desulfuricans

To explore the physiological role of tetraheme cytochrome c(3) in the sulfa te-reducing bacterium Desulfovibrio desulfuricans G20, the gene encoding th e preapoprotein was cloned, sequenced, and mutated by plasmid insertion. Th e physical analysis of the DNA from the strain carrying the integrated plas mid showed that the insertion was successful, The growth rate of the mutant on lactate with sulfate was comparable to that of the wild type; however, mutant cultures did not achieve the same cell densities. Pyruvate, the oxid ation product of lactate, served as a poor electron source for the mutant. Unexpectedly, the mutant was able to grow on hydrogen sulfate medium. These data support a role for tetraheme cytochrome c(3) in the electron transpor t pathway from pyruvate to sulfate or sulfite in D. desulfuricans G20.