Phylogenetic and physiological diversity of Arthrobacter strains isolated from unconsolidated subsurface sediments

Forty strains of Cram-positive, aerobic, heterotrophic bacteria isolated fr om saturated subsurface lacustrine, paleosol and fluvial sediments at the U S Department of Energy's Hanford Site in south central Washington State wer e characterized by phylogenetic analysis of 16S rRNA gene sequences and by determination of selected morphological, physiological and biochemical trai ts. Phylogenetic analyses of 165 rDNA sequences from subsurface isolates in the context of similar sequences from previously described bacterial speci es indicated that 38 of the subsurface strains were most closely related to Arthrobacter. The other two strains appeared to be most closely related to Kocuria. The subsurface isolates fell into seven phylogenetically coherent and distinct clusters, indicating that there was a significant degree of d iversity among them. Additional diversity was detected by analysis of cellu lar fatty acids and physiological traits. The general morphological. physio logical and biochemical traits of the subsurface strains were consistent wi th those of Arthrobacter, Micrococcus and genera recently separated from Mi crococcus, such as Kocuria, Some of the subsurface strains were phylogeneti cally closely related to certain species of Arthrobacter (16S rDNA sequence similarities > 99 %). However, most of the subsurface isolates did not clu ster with previously established species in phylogenetic analyses of 165 rR NA gene sequences or with hierarchical cluster analysis of cellular fatty a cid profiles. Moreover, many of the subsurface isolates that were most clos ely related to Arthrobacter also differed from all established species of t hat genus in several of their specific physiological characteristics. Most of the subsurface isolates, then, are likely to be novel strains or species of Arthrobacter.