Soil bacteria that also form mutualistic symbioses in plants encounter two major levels of selection. One occurs during adaptation to and survival in soil, and the other occurs in concert with host plant speciation and adaptation. Actinobacteria from the genus Frankia are facultative symbionts that form N 2 -fixing root nodules on diverse and globally distributed angiosperms in the "actinorhizal" symbioses. Three closely related clades of Frankia sp. strains are recognized; members of each clade infect a subset of plants from among eight angiosperm families. We sequenced the genomes from three strains; their sizes varied from 5.43 Mbp for a narrow host range strain (Frankia sp. strain HFPCcI3) to 7.50 Mbp for a medium host range strain (Frankia alni strain ACN14a) to 9.04 Mbp for a broad host range strain (Frankia sp. strain EAN1pec.) This size divergence is the largest yet reported for such closely related soil bacteria (97.8%-98

Frankia sp. strains are slow‐growing Actinobacteria that form N2‐fixing root nodules on certain angiosperm trees and shrubs. These organisms are generally cultured in liquid media as routine growth on solid media is impractical because of lengthy incubation periods. Liquid media is problematic for filamentous organisms because unicellular spores are difficult to isolate, and mutants are difficult to separate. The goal of this study was to optimize Frankia CcI3 growth on solid media. Starting with an appropriate basal medium containing pyruvate as a carbon source, various peptones were individually tested to determine if the time needed for colonies to appear could be reduced. Bacto™ Proteose Peptone #3 at 1.6 mg ml−1 final concentration promoted the best growth with colonies visible after 3 days, compared with the 7‐ to 10‐day incubation required for control unamended media. Gellan gum gave a more rapid growth response as compared with agar. Increased calcium concentrations were required to promote solidification of gellan gum. Sporulation occurred within 2 weeks of plating CcI3 with colonies changing color from cream to reddish‐brown. Scanning and transmission electron micrographs revealed the architecture of colonial development. Colonies developed in a lens‐shaped manner mainly by penetration into the gel. Older colonies had numerous empty hyphae with sporangia developing near or at the surface and with crystalline material, presumably pigment, interspersed among the hyphae. Occasional vesicles were seen mixed within the colonies. Colonial development of Frankia CcI3 is reminiscent of that described for other members of the filamentous Suborder Frankineae.

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We report the molecular analysis of a 130-kb DNA region containing a junction between beta and non-beta satellite DNA from chromosome 15p. The genomic region is characterized by beta satellite blocks intermingled with variants of the D4Z4 repeat, and duplicons from 4q24 and 4q35. Besides the p-arm of acrocentric chromosomes, the duplicons showed a wide genomespread involving pericentromeric, sub-telomeric, and interstitial regions. In this regard, the paralogous sequences were characterized by a high similarity index (96%), thus indicating a recent transposition during the evolution. The acrocentrics differedwith regard to the location of the 4q24 paralogous region, since it mapped on the p-arm of chromosomes 13-15 and 21, but only on 22q11.2. Conversely, the 4q35 duplication marked the p-arm of all the acrocentrics. In different individuals, the short arm of acrocentric chromosomes revealed a great variability of sequence representation and location at p11 and/or p13 for both the 4q24 and 4q35 duplications. The studied genomic region from chromosome 15p, of which a contig of approximately 200 kb has been derived, could lead to more detailed investigations into the sequence organization and possible biological function of chromosome regions that are located close to the rDNA array.

SUMMARY A new case for mosaicism for an extra small ring chromosome is described in a 13‐year‐old girl with minimal phenotypic anomalies and moderate mental retardation. The origin of the extra chromosome could not be determined either cytogenetically or clinically. The present case is compared with six similar cases in the literature. RÉSUMÉ Mosaïque avec un chromosome supplément aire en petit anneau Un nouveau cas de mosaïque avec chromosome supplementaire en petit anneau est décrit chez une fille de 13 ans présentant des anomalies phénotypiques minimes et un retard mental modéré. 'origine du chromosome supplémentaire n'a pu être déterminé cytogénétiquement ou cliniquement. Le cas présent est compareéà six cas semblables de la littérature. ZUSAMMENFASSUNG Mosaik für ein zusätzliches kleines Ringchromosom Es wird ein neuer Fall mit einem Mosaik für ein zusätzliches kleines Ringchromosom bei einem 13‐jährigen Mädchen mit geringen phänotypischen Veränderungen und mäßiger geistiger Retardierung beschrieben. Die Herkunft des zusätzlichen Chromosoms konnte weder cytogenetisch noch klinisch herausgefunden werden. Der vorliegende Fall wird mit sechs ähnlichen Fällen aus der Literatur verglichen. RESUMEN Mosaicismo por un cromosoma extra de anillo pequeño Un nuevo caso de mosaicismo por un cromosoma extra de anillo pequeño se describe en una niña de 13 años de edad con anomalías fenotípicas mínimas y un retraso mental moderado. El origen del cromosoma extra no puede ser determinado ni citogenéticamente ni clínicamente. El caso presente se compara con otros seis casos similares de la literatura.