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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.

Loss of Cytochrome c Oxidase Activity and Acquisition of Resistance to Quinone Analogs in a Laccase-Positive Variant of Azospirillum lipoferum

Gladys Alexandre,^1,2 René Bally,¹ Barry L. Taylor,² and Igor B. Zhulin^2,*

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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^* Corresponding author. Mailing address: Department of Microbiology and Molecular Genetics, School of Medicine, Loma Linda University, Loma Linda, CA 92350. Phone: (909) 558-4480. Fax: (909) 558-4035. E-mail: izhulin{at}som.llu.edu.

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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.

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