Aliidiomarina shirensis as Possible Source of the Integron- and Plasmid-Mediated Fosfomycin Resistance Gene fosC2 .

In-silico analysis and cloning experiments identified a fosC2- like fosfomycin resistance gene in the chromosome of Aliidiomarina shirensis, with our data suggesting that this bacterium might be added to the list of species identified as reservoirs of fos -like genes that were subsequently acquired by other Gram-negative species. Indeed, the fosC2 gene was identified as acquired in Providencia huaxinensis and Aeromonas hydrophila isolates, with this gene being located in class 1 integron structures in the latter cases. Biochemical characterization and site-directed mutagenesis showed a higher catalytic efficiency for the intrinsic FosC2 AS (from A. shirensis ) than for the acquired FosC2 (from P. huaxinensis ) enzyme due to a single substitution in the amino acid sequence (Gly43Glu). Notably, this study constitutes the first identification of the likely natural reservoir of a complete gene cassette (including its attC site).