Taxonomic implications of quantitative transformation in Acinetobacter calcoaceticus

Quantitative transformation of streptomycin resistance marker was carried out with strains of Acinetobacter calcoaceticus. Standard recipient strain was the competent BD4-Ss. Transformation proceeded in a liquid system with a concentration of 20 micrograms/ml of streptomycin resistant DNA (Sr-DNA) from BD4, 17 reference strains of Acinetobacter, and 42 recent clinical isolates of the acid forming variant (anitratus) and 12 of the non-acid forming variant (lwoffi) as donors of Sr-DNA. The exposure time was 20 min before interruption with DNase and quantitated plating. Among the strains examined were differentiated 16 biotypes as based on oxidative acid production from glucose and lactose, haemolysis, urease, gelatinase, and growth with citrate as the sole carbon source. Autologous transformation gave a transformation of 2.94 (+/- 0.66)% of the recipient cells (quantitated by colony forming units). Sr-DNA from 50 of 63 strains were able to transform BD4-Ss. The transformation ratio was 0.06-6.4% of autologous BD4 transformation. Two further recent clinical isolates were weakly transformation competent. Competence was only found in autologous transformation. The major portion (50/63) of the strains belong to the BD4 genotype of A. calcoaceticus, but the taxonomic position of the 13 non-donors in respect to BD4 could not be evaluated by transformation because of lack of a competent recipient. The strains transforming BD4 belonged to both the glucose acidifyers and the non-acidifyers without genetic distinction. The results are consistent with recognition of both as belonging to the same species, but with their recognition as species variants: A calcoaceticus var, anitratum and A. calcoaceticus var. lwoffi.