Metal stress selects for bacterial ARDRA-types with a reduced catabolic versatility

In a previous study, 76 out of 899 bacteria, isolated from uncontaminated and adjacent metal-contaminated experimental plots, were found to fall within 12 clusters on the basis of a fourfold ‘amplified ribosomal DNA restriction analysis’ (ARDRA). Eight of these 12 ARDRA-clusters were re-investigated in the present study by sequencing about 500 bp of the 16S rDNA of the pertaining 51 isolates. Sequencing confirmed that, with the stringent fourfold ARDRA applied, all isolates of a given ARDRA-cluster did indeed have identical 16S rDNA. Seven ARDRA-clusters had 16S rDNA similarities of 98% or more with reference species suggesting identification was at least at the genus level. With one ARDRA-cluster, having a similarity of only 93% with Sphingobacterium heparium, identification was less certain. An unequivocal assignment of the eight ARDRA-clusters to distinct species was not possible. However, similarities >99.3% of five ARDRA-clusters with five reference species from two genera suggested identification was eventually even at the species level. es of seven ARDRA-clusters from increasingly metal-contaminated soil samples were decreasingly versatile with respect to aromatic acids they could utilise as sole sources of carbon and energy. Only in one ARDRA-cluster exhibiting 99.8% similarity with Arthrobacter nicotinovorans was this effect less pronounced. The data strongly suggest that the decrease in catabolic versatility observed with metal-affected bacterial communities also applies to the genus level, if not to the species level.