Relationship between nitrite reduction and active phosphate uptake in the phosphate-accumulating denitrifier Pseudomonas sp strain JR 12

Phosphate uptake by the phosphate-accumulating denitrifier Pseudomonas sp. JR12 was examined with different combinations of electron and carbon donors and electron accepters. Phosphate uptake in acetate-supplemented cells too k place with either oxygen or nitrate but did not take place when nitrite s erved as the final electron acceptor, Furthermore, nitrite reduction rates by this denitrifier were shown to be significantly reduced in the presence of phosphate, Phosphate uptake assays in the presence of the H+-ATPase inhi bitor N,N'-dicyclohexylcarbodiimide (DCCD), in the presence of the uncouple r carbonyl cyanide 3-chlorophenylhydrazone (CCCP), or with osmotic shock-tr eated cells indicated that phosphate transport over the cytoplasmic membran e of this bacterium was mediated by primary and secondary transport systems . By examining the redox transitions of whole cells at 553 nm we found that phosphate addition caused a significant oxidation of a c-type cytochrome. Based on these findings, we propose that this c-type cytochrome serves as a n intermediate in the electron transfer to both nitrite reductase and the s ite responsible for active phosphate transport. In previous studies with th is bacterium we found that the oxidation state of this c-type cytochrome wa s significantly higher in acetate-supplemented, nitrite-respiring cells (in capable of phosphate uptake) than in phosphate-accumulating cells incubated with different combinations of electron donors and accepters. Based on the latter finding and results obtained in the present study it is suggested t hat phosphate uptake in this bacterium is subjected to a redox control of t he active phosphate transport site. By means of this mechanism an explanati on is provided for the observed absence of phosphate uptake in the presence of nitrite and inhibition of nitrite reduction by phosphate in this organi sm. The implications of these findings regarding denitrifying, phosphate re moval wastewater plants is discussed.