The membrane-bound respiratory chain of Pseudomonas pseudoalcaligenes KF707 cells grown in the presence or absence of potassium tellurite This work is dedicated to my friend and colleague Franco Tatò, prematurely deceased on 7 July 2001.

The respiratory chain of Pseudomonas pseudoalcaligenes KF707 in membranes isolated from cells grown in the presence or absence of the toxic oxyanion tellurite ( \(TeO_{3}^{2{-}}\) ) was examined. Aerobic growth in the absence of tellurite shows an NADH-dependent respiration which is 80% catalysed by the cytochrome (cyt) bc 1-containing pathway leading to two terminal membrane-bound cyt c oxidases inhibited by different concentrations of KCN (IC50 0·2 and 1 μM). A third oxidase, catalysing the remaining 20% of the cyanide-resistant respiration and fully inhibited by 2–3 mM KCN, is also present; this latter pathway accounts for 60–70% of the total NADH-dependent respiration in membranes from cells grown in LB medium supplemented with potassium tellurite (35 μg ml−1). Two high-potential b-type haems (E m,7 +395 and 318 mV) are redox centres of a membrane-bound cyt c oxidase (possibly of the cbb 3 type) which shows a 50% decrease of its activity in parallel with a similar decrease of the c-type haem content (mostly soluble cyt c) in membranes from tellurite-grown cells; the latter type of cells specifically contain a cyt b type at +203 mV (pH 9·0) which is likely to be involved in cyanide-resistant respiration. Comparison of the growth curve of KF707 cells in parallel with tellurite uptake showed that intracellular accumulation of tellurium (Te0) crystallites starts from the mid-exponential growth phase, whereas tellurite-induced changes of the respiratory chain are already evident during the early stages of growth. These data were interpreted as showing that reduction of tellurite to tellurium and tellurite-dependent modifications of the respiratory chain are unrelated processes in P. pseudoalcaligenes KF707.