Graduate Thesis Or Dissertation
 

Phosphorus metabolism in Pseudomonas stutzeri

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5138jj74h

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  • The role of nitrate oxygen as a terminal acceptor of hydrogen stands as a unique form of bacterial respiration. As nitrate is reduced to nitrite on to the gaseous state (N₂, N₂O) the substrate is oxidized to give the requisite energy for cell growth. The present study will deal with selected aspects of the energy levels gained when nitrate and molecular oxygen operate as the terminal electron acceptors. Pseudomonas stutzeri, an active nitrate reducer, was used throughout the entire study. The culture was maintained on nitrate agar. A semi-synthetic medium was used for the experimental studies. An electrolytic respirometer assembly was used for oxygen uptake and nitrogen evolution was measured using a Beckman model GC-2 chromatograph. Analyses for nitrites, total nitrogen, carbon dioxide and phosphorus were determined by established chemical procedures. Several older aspects of the problem have been clarified and new information presented. As might have been expected, large cell masses did not show a measurable uptake of phosphorus presumably because of existing cell reserves. On the other hand a growing cell system did fix significant amounts of phosphorus and when oxygen uptake was measured, applicable growth P/O ratios were obtained. The aerobic system showed a relative P/O ratio of 0.01 whereas the ratio for the anaerobic nitrate cell system was 0.0036. The observed difference in the two ratios of 2.8 approached the assumed aerobic P/O ratio of 3:1. However, when oxygen utilization and phosphorus fixation was calculated, on the basis of equivalent cell counts, then an entirely different picture emerged. In the latter case, the aerobic to anaerobic ratio became 1:1.5 rather than 3:1. If it is assumed that the aerobic system synthesizes 3 ATP molecules per atom of oxygen, then the anaerobic cells with nitrate as the final acceptor would produce 2 ATP molecules. The above results agree with present information on the electron transport system of cultures similar to Pseudomonas stutzeri.
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