A Conserved Histidine in Cytochrome c Maturation Permease CcmB of Shewanella putrefaciens Is Required for Anaerobic Growth below a Threshold Standard Redox Potential

Abstract

. Genetic complementation and nucleotide sequence analyses indicated that the CCMB1 respiratory mutant phenotype was due to mutation of a conserved histidine residue (H108Y) in a protein that displayed high homology to Escherichia coli CcmB, the permease subunit of an ABC transporter involved in cytochrome c maturation. Although CCMB1 retained the ability to grow on electron acceptors with high E 0 , the cytochrome content of CCMB1 was <10% of that of the wild-type strain. Periplasmic extracts of CCMB1 contained slightly greater concentrations of the thiol functional group (-SH) than did the wild-type strain, an indication that the E h of the CCMB1 periplasm was abnormally low. A ccmB deletion mutant was unable to respire anaerobically on any electron acceptor, yet retained aerobic respiratory capability. These results suggest that the mutation of a conserved histidine residue (H108) in CCMB1 alters the redox homeostasis of the periplasm during anaerobic growth on electron acceptors with low (but not high) E 0 . This is the first report of the effects of Ccm deficiencies on bacterial respiration of electron acceptors whose E 0 nearly span the entire redox continuum.

Anaerobic Respiration of Elemental Sulfur and Thiosulfate by Shewanella oneidensis MR-1 Requires psrA , a Homolog of the phsA Gene of Salmonella enterica Serovar Typhimurium LT2

“…The reasons for this finding are not clear, but it may be due to repression of the Psr system by residual (1 mM) S 4 O 6 2Ϫ remaining in the system. A similar growth pattern was recently reported for cytochrome c maturation (ccmB) mutants of S. putrefaciens 200 that are unable to reduce NO 2 Ϫ but retain NO 3 Ϫ reduction activity (11). The S. putrefaciens CCMB1 mutant (with an in-frame deletion of ccmB) stoichiometrically converts NO 3 Ϫ to NO 2 Ϫ but is unable to respire the produced NO 2 Ϫ , and growth halts.…”

“…The majority of studies of anaerobic respiration by S. oneidensis have focused on the mechanism of electron transport to transition metals and radionuclides, while the mechanism of electron transport to metalloids such as inorganic sulfur compounds remains poorly understood (8,11,14,46,56). Previous studies demonstrated that several members of the Shewanella genus couple the oxidation of organic matter (or hydrogen) to the dissimilatory reduction of S 0 , a process that does not require direct contact between the cell and the S 0 particle (41,47) (Fig.…”

“…Shewanella oneidensis MR-1, a facultatively anaerobic gammaproteobacterium, respires a variety of compounds as an anaerobic electron acceptor, including the inorganic sulfur compounds S 0 , SO 3 2Ϫ , S 2 O 3 2Ϫ , and S 4 O 6 2Ϫ ; transition metals [e.g., Fe(III) and Mn(IV)]; and radionuclides [e.g., U(VI) and Tc(VII)] (8,21,41,44,50,55,56). The majority of studies of anaerobic respiration by S. oneidensis have focused on the mechanism of electron transport to transition metals and radionuclides (11,14,34,46,58,59), while the mechanism of electron transport to inorganic sulfur compounds has not been thoroughly examined.…”

Siderophores Are Not Involved in Fe(III) Solubilization during Anaerobic Fe(III) Respiration by Shewanella oneidensis MR-1

“…Mn(III) reduction was monitored colorimetrically by filtering samples through a disposable nylon filter with a pore size of 0.22 m (Millex) and subsequently monitoring absorbance spectrophotometrically at 480 nm (31). Mn(IV) reduction was monitored by mixing samples at a 1:9 ratio with 2 mM benzidine in a 10% acetic acid solution and monitoring absorbance spectrophotometrically at 424 nm (7,14). Fe(III) reduction rates were determined by monitoring Fe(II) production over time via HCl extraction, followed by a Ferrozine colorimetric assay (35,58).…”

“…Fe(III) reduction rates were determined by monitoring Fe(II) production over time via HCl extraction, followed by a Ferrozine colorimetric assay (35,58). Cell growth was monitored by direct cell counts of acridine orange-stained cells via epifluorescence microscopy (Carl Zeiss AxioImager Z1 microscope) (8,14).…”