Amplified rDNA restriction analysis and further genotypic characterisationof metal-resistant soil bacteria and related facultative hydrogenotrophs

The level of genotypic relationship between czc(+) soil bacteria mainly res istant to zinc (but also to various other metals), and related facultative hydrogenotrophs previously assigned to the genera Alcaligenes, Ralstonia, a nd Burkholderia was evaluated using ARDRA (Amplified Ribosomal DNA Restrict ion Analysis). The analysis included 44 strains isolated from harsh industr ial environments in sediments, soils and wastes with high content of heavy metals. These strains were selected by their ability to grow in the presenc e of high concentrations of multiple heavy metals and to hybridise with czc or ncc probes. The czc operon confers resistance to cadmium, zinc and coba lt in strain Ralstonia eutropha CH34. The ncc operon confers resistance to nickel, cobalt and cadmium in strain 31A known as Alcaligenes xylosoxidans. The analysis showed a close phylogenetic clustering of the czc(+) strains i nside the Ralstonia genus despite of their different origins and that the R alstonia genus contained also the hydrogenotrophs and some catabolic strain s assigned to the genus Ralstonia eutropha, strains up to now registrated a s CDC IV c-2 strains as well as reference strains belonging to Ralstonia so lanacearum and Ralstonia pickettii. The ncc(+) strains are phylogenetically less related to each other compared to the czc(+) strains. This suggests that the tested czc(+) strains and some of the ncc(+) strains may be considered as belonging to the genus Ralstonia. Inside this major R alstonia cluster, a subcluster gathers most of the czc(+) isolates maybe gi ving a clue to define a new species. Besides, from 30 tested strains, 15 me tal resistant strains of this subcluster proved to display the unusual muta tor phenotype characteristic of the representative strain CH34.