Journal of Bacteriology, November 1999, p. 6730-6738, Vol. 181, No. 21
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Laboratoire d'Ecologie Microbienne du Sol, CNRS-UMR 5557, l'Universite Claude-Bernard, 69622 Villeurbanne Cedex, France,1 and Department of Microbiology and Molecular Genetics, School of Medicine, Loma Linda University, Loma Linda, California 923502
Received 26 April 1999/Accepted 23 August 1999
Laccase, a p-diphenol oxidase typical of plants and fungi, has been found recently in a proteobacterium, Azospirillum lipoferum. Laccase activity was detected in both a natural isolate and an in vitro-obtained phase variant that originated from the laccase-negative wild type. In this study, the electron transport systems of the laccase-positive variant and its parental laccase-negative forms were compared. During exponential (but not stationary) growth under fully aerobic (but not under microaerobic) conditions, the laccase-positive variant lost a respiratory branch that is terminated in a cytochrome c oxidase of the aa3 type; this was most likely due to a defect in the biosynthesis of a heme component essential for the oxidase. The laccase-positive variant was significantly less sensitive to the inhibitory action of quinone analogs and fully resistant to inhibitors of the bc1 complex, apparently due to the rearrangements of its respiratory system. We propose that the loss of the cytochrome c oxidase-containing branch in the variant is an adaptive strategy to the presence of intracellular oxidized quinones, the products of laccase activity.
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