16S rDNA analysis for characterization of denitrifying bacteria isolated from three agricultural soils

Bacteria capable of denitrification are spread among phylogenetically diver se groups. In the present investigation, molecular methods (amplified ribos omal DNA restriction analysis (ARDRA) and partial 16S rDNA gene sequencing) were used to determine the genetic diversity of culturable denitrifying so il bacteria. The purpose of this work was to study the microbial density an d diversity of denitrifying communities isolated from two luvisols and a re ndosol. The denitrifying bacterial density was significantly higher in the two luvisols (3 x 10(6) and 4 x 10(6) bacteria g(-1) dry soil) than in the rendosol (4 x 10(5) bacteria g(-1) dry soil). Denitrifying isolates from so ils were grouped according to the similarity of their restriction patterns into 26 ARDRA types. Interestingly ARDRA analysis suggests that some denitr ifying isolates are specific to a soil type while others seem to be geograp hically widespread. The number of individual isolates found in each ARDRA t ype appeared to be highly variable between the two sampling dates but some denitrifying types were capable of persisting in soil. The tree obtained fr om the partial sequences revealed five major branches exhibiting highest id entity to the following genera: (i) Burkholderia-Ralstonia, (ii) Pseudomona s, (iii) Xanthomonas-Frateuria, (iv) Bacillus and (v) Streptomyces. Our 16S rDNA-based analysis clearly reveals broad diversity exceeding that previou sly described in the literature. (C) 2000 Federation of European Microbiolo gical Societies. Published by Elsevier Science B.V. Ail rights reserved.