NICKEL-RESISTANT BACTERIA FROM ANTHROPOGENICALLY NICKEL-POLLUTED AND NATURALLY NICKEL-PERCOLATED ECOSYSTEMS

DNA fragments harboring the nickel resistance determinants from bacter ia isolated from anthropogenically polluted ecosystems in Europe and Z aire were compared with those harboring the nickel resistance determin ants from bacteria isolated from naturally nickel-percolated soils fro m New Caledonia by DNA-DNA hybridization. The biotinylated DNA probes were derived from the previously described Alcaligenes eutrophus CH34, Alcaligenes xylosoxidans 31A, Alcaligenes denitrificans 4a-2, and Kle bsiella oxytoca CCUG 15788 and four new nickel resistance-determining fragments cloned from strains isolated from soils under nickel-hyperac cumulating trees. Nine probes were hybridized with endonuclease-cleave d plasmid and total DNA samples from 56 nickel-resistant strains. Some of the New Caledonian strains were tentatively identified as Acinetob acter, Pseudomonas mendocina, Comamonas, Hafnia alvei, Burkholderia, A rthrobacter aurescens, and Arthrobacter ramosus strains. The PNA of mo st strains showed homologies to one or several of the following nickel resistance determinants: the cnr and ncc operons of the strains A. eu trophus CH34 and A. xylosoxidans 31A, respectively, the nre operon of strain 31A, and the nickel resistance determinants of K. oxytoca. On t he basis of their hybridization reactions the nickel resistance determ inants of the strains could be assigned to four groups: (i) cnr/ncc ty pe, (ii) cnr/ncc/nre type, (iii) K. oxytoca type, and (iv) others. The majority of the strains were assigned to the known groups. Among the strains from Belgium and Zaire, exclusively the cnr/ncc and the cnr/nc c/nre types were found. Among the New Caledonian strains all four type s were represented. Homologies to the nre operon were found only in co mbination with the cnr/ncc operon. The homologies to the cnr/ncc opero n were the most abundant and were detected alone or together with homo logies to the nre operon. Only the DNA of the strains isolated from so il in Scotland and the United States and that of five of the New Caled onian strains did not show any detectable homologies to any of our pro bes. The nickel resistance fragment isolated from Burkholderia strain 32W-2 was studied in some detail. This 15-kb BamHI fragment conferred resistance to 1 to 5 mM NiCl2, to Escherichia coli and resistance to u p to 25 mM NiCl2, to A. eutrophus. It showed strong homologies to both the cnr/ncc operon and the nre operon and conferred strictly regulate d (inducible) nickel resistance to A. eutrophus.