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Appl. Environ. Microbiol., Nov 1995, 3998-4003, Vol 61, No. 11
Copyright © 1995, American Society for Microbiology

Alternative Function of the Electron Transport System in Azotobacter vinelandii: Removal of Excess Reductant by the Cytochrome d Pathway

J Liu, F Lee, C Lin, X Yao, JW Davenport and T Wong
Institute of Life Sciences, and Department of Marine Resources, National Sun Yet-Sen University, Taiwan, Republic of China, and Molecular Sciences and Microbiology, University of Memphis, Memphis, Tennessee 38152

The N(inf2)-fixing bacterium Azotobacter vinelandii was grown in an O(inf2)-regulated chemostat with glucose or galactose as substrate. Increasing the O(inf2) partial pressure resulted in identical synthesis of the noncoupled cytochrome d terminal oxidase, which is consistent with the hypothesis that A. vinelandii uses high rates of respiration to protect the nitrogenase from oxygen. However, cell growth on glucose showed a lower yield of biomass, higher glycolytic rate, higher respiratory rate, and lower cytochrome o content than cell growth on galactose. Elemental analysis indicated no appreciable change in the C-to-N ratio of cell cultures, suggesting that the major composition of the cell was not influenced by the carbon source. A poor coordination of glucose and nitrogen metabolisms in A. vinelandii was suggested. The rapid hydrolysis of glucose resulted in carbonaceous accumulation in cells. Thus, Azotobacter species must induce a futile electron transport to protect cells from the high rates of glucose uptake and glycolysis.

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