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Applied and Environmental Microbiology, June 2007, p. 3556-3565, Vol. 73, No. 11
0099-2240/07/$08.00+0     doi:10.1128/AEM.02678-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Clonothrix fusca Roze 1896, a Filamentous, Sheathed, Methanotrophic -Proteobacterium ^,

Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università degli Studi di Lecce, Via Monteroni, 73100 Lecce,¹ Dipartimento di Scienze Ambientali, Seconda Università degli Studi di Napoli, Via A. Vivaldi 43, 81100 Caserta,² Istituto di Genetica e Biofisica Adriano Buzzati-Traverso, Consiglio Nazionale delle Ricerche, Via Pietro Castellino 111, 80131 Napoli,³ Istituto Motori, Consiglio Nazionale delle Ricerche, Viale Marconi 8, 80125 Napoli, Italy⁴

Received 16 November 2006/ Accepted 2 April 2007

Crenothrix polyspora Cohn 1870 and Clonothrix fusca Roze 1896 are two filamentous, sheathed microorganisms exhibiting complex morphological differentiation, whose phylogeny and physiology have been obscure for a long time due to the inability to cultivate them. Very recently, DNA sequencing data from uncultured C. polyspora-enriched material have suggested that Crenothrix is a methane-oxidizing -proteobacterium (39). In contrast, the possible ecological function of C. fusca, originally considered a developmental stage of C. polyspora, is unknown. In this study, temporal succession of two filamentous, sheathed microorganisms resembling Cohn's Crenothrix and Roze's Clonothrix was observed by analyzing the microbial community of an artesian well by optical microscopy. Combined culture-based and culture-independent approaches enabled us to assign C. fusca to a novel subgroup of methane-oxidizing -proteobacteria distinct from that of C. polyspora. This assignment was supported by (i) methane uptake and assimilation experiments, (ii) ultrastructural data showing the presence in C. fusca cytoplasm of an elaborate membrane system resembling that of methanotrophic -proteobacteria, and (iii) sequencing data demonstrating the presence in its genome of a methanol dehydrogenase subunit-encoding gene (mxaF) and a conventional particulate methane mono-oxygenase subunit-encoding gene (pmoA) that is different from the unusual pmoA (u-pmoA) of C. polyspora.

Published ahead of print on 6 April 2007.

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