Arthrobacter sp. strain FB24 was isolated from chromate and xylene enriched soil microcosms used to ascertain changes in microbial community composition under these stresses (Nakatsu et al., submitted). The soil used in the microcosms had long been polluted with heavy metals (chromate, lead) and aromatic hydrocarbons (toluene, xylene, benzene) (Joynt et al., submitted). The enrichment used in the microcosms selected for a relatively small number of phylotypes, and Arthrobacter and other Actinobacteria were commonly found using cultivation and non-cultivation based analysis methods.   This particular isolate peaked our interest because of its extreme chromium tolerance (300 mM Cr 6+ ).   It was subsequently found to be resistant to other metals, able to degrade some hydrocarbons and also appears to be radiation resistant.   In general, Arthrobacter species are apparently ubiquitous soil bacteria that have been studied because of their vast metabolic activities and survival in extreme environments.   They are aerobic, high GC Gram positive bacteria, with nutritional versatility using a range of carbon sources, and most often recognized morphologically by their jointed-rod to coccus growth cycle. They are classified into the class Actinobacteria, order Actinomycetales, and family Micrococcaceae. There are two accepted major phylogenetic clades within the Arthrobacter genus, the A. globiformis/A. citreus group and the A. nicotianae group (Jones & Keddie, 1999-2003) . These groups differ in their peptidoglycan structure, teichoic acid content, and lipid composition.   The 16 rRNA gene sequence indicates that strain FB24 falls into the A. globiformis/A. citreus group with the closest sequence being from A. globiformis (98% identity).   Although Arthrobacter species have often been found in diverse environments and are readily cultivated studies of it in any depth are limited.

Jones, D. & R. M. Keddie. 1999-2003. The Genus Arthrobacter . In The prokaryotes [electronic resource]: an evolving electronic resource for the microbiological community. Edited by M. Dworkin. New York: Springer-Verlag.

Joynt, J., M. Bischoff, R. Turco, A. Konopka, and C. H. Nakatsu.   Microbial community analysis of soils contaminated with lead, chromium and organic solvents. (submitted).

Nakatsu, C. H., N. Carmosini, B. Baldwin, F. Beasley, P. Kourtev, and A. Konopka. Soil microbial community responses to additions of organic carbon substrates and heavy metals (Pb and Cr). Submitted.