Artifacts associated with the use of thiocyanate and valinomycin/K+ as permeant ions in oxidant pulse experiments on denitrifying bacteria

Bioenergetic examination of the heterotrophic nitrifier-denitrifier Thiosphaera pantotropha

The heterotrophic nitrifying-denitrifying bacterium Thiosphaera pantotropha is remarkable as it nitrifies and denitrifies simultaneously. With respect to nitrogenous compounds, whether nitrification or denitrification results in energy conservation is of interest. Proton translocation studies were performed to determine if energy was conserved by the bacterium during heterotrophic nitrification and denitrification. Hydrazine (N2H5+) was employed as the heterotrophic nitrification substrate while nitrate, nitrite and nitrous oxide were used as denitrification substrates. Analysis of the data indicate that the bacterium does not conserve energy when hydrazine was the substrate. Conversely, energy was conserved when either nitrate, nitrite or nitrous oxide functioned as the oxidants during denitrification-dependent proton translocation experiments. Thiosphaera pantotropha thus is similar to other heterotrophic nitrifiers-denitrifiers in that it conserves energy while denitrifying but has not been observed to do so when heterotrophically nitrifying.

Respiration-linked proton translocation coupled to anaerobic reduction of manganese(IV) and iron(III) in Shewanella putrefaciens MR-1

An oxidant pulse technique, with lactate as the electron donor, was used to study respiration-linked proton translocation in the manganese- and iron-reducing bacterium Shewanella putrefaciens MR-1. Cells grown anaerobically with fumarate or nitrate as the electron acceptor translocated protons in response to manganese (IV), fumarate, or oxygen. Cells grown anaerobically with fumarate also translocated protons in response to iron(III) and thiosulfate, whereas those grown with nitrate did not. Aerobically grown cells translocated protons only in response to oxygen. Proton translocation with all electron acceptors was abolished in the presence of the protonophore carbonyl cyanide m-chlorophenylhydrazone (20 microM) and was partially to completely inhibited by the electron transport inhibitor 2-n-heptyl-4-hydroxyquinoline N-oxide (50 microM).

Growth of Pseudomonas aeruginosa on nitrous oxide

Three strains of Pseudomonas aeruginosa were grown anaerobically on exogenous N2O in a defined medium under conditions that assured the maintenance of highly anaerobic conditions for periods of 1 week or more. The bacteria were observed reproducibly to increase their cell density by factors of 3 to 9, but not more, depending on the initial amount of N2O. Growth on N2O was cleanly blocked by acetylene. Cell yields, CO2 production, and N2O uptake all increased with initial PN2O at PN2O less than or equal to 0.1 atm. Growth curves were atypical in the sense that growth rates decreased with time. This is the first observation of growth of P. aeruginosa on N2O as the sole oxidant. N2O was shown to be an obligatory, freely diffusible intermediate during growth of strains PAO1 and P1 on nitrate. All three strains used this endogenous N2O efficiently for growth. For strains PAO1 and P1, it was confirmed that exogenous N2O had little effect on the cell yields of cultures growing with nitrate; thus, for these strains exogenous N2O neither directly inhibited growth nor was used significantly for growth. On the other hand, strain P2 grew abundantly on exogenous N2O when small and growth-limiting concentrations of nitrate or nitrate (2 to 10 mM) were included in the medium. The dramatic effect of these N-anions was realized in large part even when the exogenous N2O was introduced immediately after the quantitative conversion of anion-nitrogen to N2. No evidence was found for a factor in filter-sterilized spent medium that stimulated fresh inocula to grow abundantly on N2O.(ABSTRACT TRUNCATED AT 250 WORDS)

Respiration-linked proton flux in Wolinella succinogenes during reduction of N-oxides

Formate uncoupled proton translocation in formate-grown Wolinella succinogenes cells supplied with N-oxides as terminal electron acceptors. In suspensions containing KSCN (but not valinomycin), H2 supported proton translocation when NO3-, NO2-, and NO were provided as oxidants. H+/N-oxide ratios were 4.77 for NO3-, 2.49 for NO2-, and 1.75 for NO. KSCN inhibits N2O reduction thus precluding use of N2O as oxidant. Repeated exposure of cells to NO inhibited their ability to translocated protons with NO as oxidant but only slightly diminished and did not eliminate their capacity for NO3(-)- or NO2(-)-dependent proton flux. Substituting reduced benzyl viologen for H2 and measuring proton uptake provided results consistent with an extramembranal location for the N- oxide reductases. The uncoupler, carbonyl cyanide m-chlorophenylhydrazone, collapsed proton gradients, permitted uptake of 2 mol H+/mol NO3- or NO2-, but unaccountably inhibited NO3- reduction by 50% while leaving H+ uptake stoichiometry of the cells unaffected.

Proton translocation during denitrification by a nitrifying--denitrifying Alcaligenes sp

A heterotrophic nitrifying Alcaligenes sp. from soil was grown as a denitrifier on nitrate and subjected to oxidant pulse experiments to ascertain the apparent efficiencies of proton translocations during O2 and nitrogen-oxide respirations. With endogenous substrate as the reducing agent the leads to H+/2e- ratios, extrapolated to zero amount of oxidant per pulse, were 9.4, 3.7, 4.3 and 3.5 for O2, nitrate, nitrite and N2O, respectively. The value for O2 and those for the N-oxides are, respectively, somewhat larger and smaller than corresponding values for Paracoccus denitrificans. None of the three permeant ions employed with the Alcaligenes sp. (valinomycin-K+, thiocyanate and triphenylmethylphosphonium) was ideal for all purposes. Thiocyanate provided highest ratios for O2 but abolished the oxidant pulse response for nitrate and N2O. Valinomycin was slow to penetrate to the cytoplasmic membrane and relatively high concentrations were required for optimal performance. Triphenylmethylphosphonium enhanced passive proton permeability and diminished proton translocation at concentrations required to realize the maximal oxidant pulse response.