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J Bacteriol, April 1998, p. 2133-2136, Vol. 180, No. 8
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Availability of O2 as a Substrate in the Cytoplasm of Bacteria under Aerobic and Microaerobic Conditions

Tanja Arras, Jan Schirawski, and Gottfried Unden*

Institut für Mikrobiologie und Weinforschung, Universität Mainz, 55099 Mainz, Germany

Received 5 December 1997/Accepted 17 February 1998

The growth rates of Pseudomonas putida KT2442 and mt-2 on benzoate, 4-hydroxybenzoate, or 4-methylbenzoate showed an exponential decrease with decreasing oxygen tensions (partial O2 tension [pO2] values). The oxygen tensions resulting in half-maximal growth rates were in the range of 7 to 8 mbar of O2 (corresponding to 7 to 8 µM O2) (1 bar = 105 Pa) for aromatic compounds, compared to 1 to 2 mbar for nonaromatic compounds like glucose or succinate. The decrease in the growth rates coincided with excretion of catechol or protocatechuate, suggesting that the activity of the corresponding oxygenases became limiting. The experiments directly establish that under aerobic and microaerobic conditions (about 10 mbar of O2), the diffusion of O2 into the cytoplasm occurs at high rates sufficient for catabolic processes. This is in agreement with calculated O2 diffusion rates. Below 10 mbar of O2, oxygen became limiting for the oxygenases, probably due to their high Km values, but the diffusion of O2 into the cytoplasm presumably should be sufficiently rapid to maintain ambient oxygen concentrations at oxygen tensions as low as 1 mbar of O2. The consequences of this finding for the availability of O2 as a substrate or as a regulatory signal in the cytoplasm of bacterial cells are discussed.

* Corresponding author. Mailing address: Institut für Mikrobiologie und Weinforschung, Universität Mainz, Becherweg 15, 55099 Mainz, Germany. Phone: 49-6131-393550. Fax: 49-6131-392695. E-mail: unden{at}mzdmza.zdv.uni-mainz.de.




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