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Applied and Environmental Microbiology, February 2004, p. 991-998, Vol. 70, No. 2
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.2.991-998.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Selection of Unusual Actinomycetal Primary {sigma}70 Factors by Plant-Colonizing Frankia Strains

Céline Lavire, Didier Blaha, and Benoit Cournoyer*

Research Group on Opportunistic Pathogens and the Environment, Ecologie Microbienne (Center for Microbial Ecology), UMR CNRS 5557-Université Claude Bernard-Lyon 1, USC INRA 1193, 69622 Villeurbanne Cedex, France

Received 4 June 2003/ Accepted 31 October 2003

Functional adaptations of {sigma}70 transcriptional factors led to the emergence of several paralogous lineages, each one being specialized for gene transcription under particular growth conditions. Screening of a Frankia strain EaI-12 gene library by {sigma}70 DNA probing allowed the detection and characterization of a novel actinomycetal primary (housekeeping) {sigma}70 factor. Phylogenetic analysis positioned this factor in the RpoD cluster of proteobacterial and low-G+C-content gram-positive factors, a cluster previously free of any actinobacterial sequences. {sigma}70 DNA probing of Frankia total DNA blots and PCR screening detected one or two rpoD-like DNA regions per species. rpoD matched the conserved region in all of the species tested. The other region was found to contain sigA, an alternative primary factor. sigA appeared to be strictly distributed among Frankia species infecting plants by the root hair infection process. Both genes were transcribed by Frankia strain ACN14a grown in liquid cultures. The molecular phylogeny of the {sigma}70 family determined with Frankia sequences showed that the alternative actinomycetal factors and the essential ones belonged to the same radiation. At least seven distinct paralogous lineages were observed among this radiation, and gene transfers were detected in the HrdB actinomycetal lineage.

* Corresponding author. Mailing address: Ecologie Microbienne, UMR CNRS 5557-Université Claude Bernard-Lyon 1, USC INRA 1193, 43 Bd. 11 Novembre 1918, BÂt. Gregor Mendel (741), 5th Floor, F-69622 Villeurbanne Cedex, France. Phone: 33 (0) 4 72 43 14 95. Fax: 33 (0) 4 72 43 12 23. E-mail: cournoye{at}biomserv.univ-lyon1.fr.

Applied and Environmental Microbiology, February 2004, p. 991-998, Vol. 70, No. 2
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.2.991-998.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.





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