MOBILE GENETIC ELEMENTS OF FUSOBACTERIUM-NUCLEATUM

The gram-negative anaerobic bacterium, Fusobacterium nucleatum, is a p redominant member of the human oral flora. As a major component of sub gingival plaque, this bacterium has a significant impact on the ecolog y of the oral cavity due to its ability to adhere to many different mi crobial species. The objective of this study was to identify and chara cterize plasmids and transposons that may have the potential to be dev eloped into tools for cloning, genetic transformation, and mutagenesis of oral isolates of F. nucleatum. Analysis of a collection of laborat ory strains resulted in the identification of a homologous family of s mall cryptic plasmids. Plasmids within this family ranged in size from 6.0 to 6.6 kb. Eighteen percent of all strains examined (n = 74) cont ained DNA sequences related to the plasmids. Homologous plasmid sequen ces were found in strains belonging to 2 of the 3 subspecies of the ba cterium. The 2 smallest plasmid species were cloned in Escherichia col i to facilitate endonuclease restriction mapping. Among the strains ex amined for plasmids, 5 exhibited resistance to at least 10 mu g/ml of tetracycline. These strains, all members of the subsp. polymorphum, co ntained a tetracycline resistance determinant (TetM) as part of a Tn91 6-like integrated transposon sequence. The Tn916-like element and 1 of the plasmid species co-resided in a single strain of the bacterium. H ybridization patterns of the Tn916-like sequences were identical in al l 5 tetracycline-resistant strains. However, these strains appeared to be clonally distinct based on genomic fingerprinting. (C) 1995 Academ ic Press, Inc.