Bacterial terminal oxidases

Changes in cytochrome content and electron transport patterns in Pseudomonas putida as a function of growth phase

Optical absorbance difference spectra of membrane vesicles prepared from aerobically grown Pseudomonas putida indicated that, when harvested in logarithmic phase, the cells contained one c-type cytochrome and two or three b-type cytochromes, one of which was cytochrome o. As the cells grew into stationary phase and the oxygen concentration of the medium dropped to essentially zero, an additional component believed to be cytochrome d was produced. Both the o- and d-type cytochromes might function as terminal oxidases. No a-type cytochromes could be detected at any stage of growth. Polarographic measurement of oxygen utilization revealed that cyanide and azide are effective inhibitors of the oxidation of ascorbate coupled with 2,6-dichlorophenolindophenol or N,N,N',N'-tetramethyl-p-phenylenediamine in respiratory particles from either log-phase or stationary-phase cells. Reduced nicotinamide adenine dinucleotide- or succinate-dependent oxygen utilization, however, was sensitive to these inhibitors only in log-phase particles. These results indicate that an alternate terminal oxidase may be synthesized by this organism in response to restricted oxygen availability and that branching of the respiratory system may result.

Use of a quantitative oxidase test for characterizing oxidative metabolism in bacteria

It was possible to quantitate the terminal oxidase(s) reaction using bacterial resting-cell suspensions and demonstrate the usefulness of this reaction for taxonomic purposes. Resting-cell suspensions of physiologically diverse bacteria were examined for their capabilities of oxidizing N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) using a manometric assay. For organisms having this capability, it was possible to calculate the conventional TMPD oxidase Q(O2) value (microliters of O2 consumed per hour per milligram [dry weight]). All cultures were grown heterotrophically at 30 C, under identical nutritional conditions, and were harvested at the late-logarithmic growth phase. The TMPD oxidase Q(O2) values showed perfect correlation with the Kovacs oxidase test and, in addition, it was possible to define quantitatively that point which separated oxidase-positive from oxidase-negative bacteria. Oxidase-negative bacteria exhibited a TMPD oxidase Q(O2) value (after correcting for the endogenous by substraction) of less than or equal 33 and had an uncorrected TMPD/endogenous ratio of less than or equal 5. The TMPD oxidase Q(O2) values were also correlated with the data obtained for the Hugh-Leifson Oxferm test. In general, bacteria that exhibited a respiratory mechanism had high TMPD oxidase values, whereas fermentative organsims had low TMPD oxidase activity. All exceptions to this are noted. This quantitative study also demonstrated that organisms that (i) lack a type c cytochrome, or (ii) lack a cytochrome-containing electron transport system, like the lactic acid bacteria, exhibited low or negligible TMPD oxidase Q(O2) values. From the 79 bacterial species (36 genera) examined, it appears that this quantitative oxidase test has taxonomic value that can differentiate the oxidative relationships between bacteria at the subspecies, species, and genera levels.