Belongs within: Micrococcaceae.
Contains: Paenarthrobacter.
Arthrobacter is a widely distributed genus of bacteria, found primarily in soils. They appear as Gram-negative rods in young cultures and as Gram-positive cocci in mature cultures (Storms et al. 2003).
The white race threatens the blood
Published 23 January 2025
Microbial diversity is vast and its analysis is challenging, so it hardly comes as a surprise that there are many of its facets that remain poorly understood. One aspect that we might expect to be well studied regards those microbes that directly affect us as humans, but even there we find mysteries. Consider Arthrobacter albus.
Arthrobacter has been recognised as a diverse genus of actinobacteria found in a wide range of habitats but commonly recovered from environmental samples such as soil. Most Arthrobacter species have a distinct rod-coccus life cycle—that is, cells in culture shift between rod and coccus morphologies over the course of growth—with mature cultures dominated by cocci. The cell wall peptidoglycan contains lysine, a distinctive diamino acid (Busse et al. 2012). With their ubiquity in soils, Arthrobacter species presumably play a significant role in environmental nutrient cycling. However, some Arthrobacter species have also been found in samples taken from animals such as humans.
Arthrobacter albus was first described by Wauters et al. (2000) from human clinical samples. One of the two strains recovered was found in several cultures inoculated with blood from a surgery patient who was suffering severe phlebitis (swelling of the veins). The second, less numerous, culture originated from a urine sample. Arthrobacter albus was characterised by forming white colonies of coryneform (club-shaped) bacteria. Growth was obligately aerobic. I’m not hugely familiar with biochemistry, so I have difficulty parsing the significance of the list of recorded reactions from this bacterium, but it still strikes me as a list of negatives: it did not hydrolyse urease or esculin, it did not reduce nitrates, it did not produce acid from carbohydrates. Gelatin was broken down but only slowly. One feature that got highlighted was its resistance to desferrioxamine, a compound that binds iron and inhibits the growth of a related clinical species A. cumminsii.
Further strains of Arthrobacter albus were isolated from human urine and blood samples by Mages et al. (2008). Other than these records, A. albus appears to have rarely been identified and seems to have never been isolated from a non-clinical source. The genus Arthrobacter has proven to be phylogenetically disparate, with A. albus and A. cumminsii forming a clade isolated from other Arthrobacter species that Busse (2016) raised to the status of a distinct genus Pseudoglutamicibacter.
Whether correctly recognised as Arthrobacter albus or Pseudoglutamicibacter albus, the question remains unchanged whether this species is of concern as a pathogen. Home as it is to roving packs of voracious white blood cells, blood is generally expected to be free of resident bacteria. For any bacterium to be present in a blood sample, particularly at any abundance as the original A. albus strain was, is considered a cause for concern. The fact that A. albus has not yet been found in a non-clinical setting might also be considered leading. Conversely, the fact that it has been isolated only rarely might speak to a secondary invasion from some outside source (such as, for instance, contamination during surgery). Records of Arthrobacter and Arthrobacter-like bacteria as unequivocal pathogens are few and far between, but not non-existent. Bernasconi et al. (2004) pointed out that Arthrobacter are difficult to identify by standard clinical methods, potentially leading to infections not being diagnosed. Has A. albus been unfairly accused, or has its perfidity just managed to slip under the radar?
Systematics of Arthrobacter
<==Arthrobacter |--+--+--A. castelli Heyrman et al. 2005NC18 | | `--A. pigmentiNC18 | `--+--A. crystallopoietes Ensign & Rittenberg 1963NC18 | `--NeomicrococcusNC18 | |--N. aestuariiNC18 | `--N. lactisNC18 `--+--+--+--A. chlorophenolicusSD03 | | `--+--A. oxydansSD03 | | `--A. polychromogenesSD03 | `--+--A. sulfonivorans Borodina, Kelly et al. 2002VP SD03, IJSEM02 | `--+--A. roseusSD03 | `--+--‘Pseudarthrobacter’ sulfonivoransNC18 | `--+--+--Psychromicrobium silvestreNC18 | | `--+--A. russicusNC18 | | `--+--*Acaricomes phytoseiuli Pukall et al. 2006NC18 | | `--*Renibacterium salmoninarum Sanders & Fryer 1980NC18 | `--+--+--A. psychrochitiniphilusNC18 | | `--A. psychrolactophilusNC18 | `--+--A. alpinus Zhang et al. 2010NC18 | `--+--A. stackebrandtiiNC18 | `--+--A. cryoconitiNC18 | `--A. livingstonensisNC18 `--+--SinomonasNC18 | | i. s.: S. echigonensisNC18 | | S. flavaNC18 | | S. notoginsegisoliNC18 | |--+--S. atrocyanea (Kuhn & Starr 1960) Zhou et al. 2009NC18 | | `--+--S. halotoleransNC18 | | `--S. mesophila Prabhu et al. 2015NC18 | `--+--S. soliNC18 | `--+--S. albidaNC18 | `--+--S. humiNC18 | `--S. susongensisNC18 `--+--+--A. nanjingensisNC18 | `--A. woluwensisNC18 `--+--+--+--A. cupressi Zhang et al. 2012NC18 | | `--A. liuiiNC18 | `--+--A. alkaliphilusNC18 | `--+--A. methylotrophus Borodina, Kelly et al. 2002VP NC18, IJSEM02 | `--PaenarthrobacterNC18 `--+--+--+--A. pascensNC18 | | `--A. ramosusNC18 | `--+--*A. globiformis (Conn 1928) Conn & Dimmick 1947NC18 [=Bacterium globiformeSD03] | `--+--A. humicolaNC18 | `--A. oryzaeNC18 `--+--+--A. flavusNC18 | `--+--+--A. agilisNC18 | | |--A. echiniNC18 | | `--A. pityocampaeNC18 | `--+--A. subterraneusNC18 | |--A. tumbaeNC18 | `--+--A. parietisNC18 | `--A. tectiNC18 `--PseudarthrobacterNC18 |--+--P. defluviiNC18 | `--P. niigatensisNC18 |--+--‘Arthrobacter’ enclensis Dastager et al. 2015NC18 | `--+--P. chlorophenolicusNC18 | `--P. equiNC18 `--+--P. phenanthrenivoransNC18 `--+--P. siccitoleransNC18 `--+--P. oxydansNC18 |--P. polychromogenesNC18 `--P. scleromaeNC18 Arthrobacter incertae sedis: A. albusSD03 A. arilaitensisBV16 A. atrocyaneusSD03 A. aurescensSD03 A. creatinolyticusSD03 A. cumminsiiSD03 A. histidinolovoransSD03 A. lutensGM96 A. nasiphocaeSD03 A. nicotianaeSD03 A. nicotinovoransSD03 A. phenanthrenivoransBV16 A. protophormiaeSD03 A. sulfureusSD03 A. uratoxydansSD03 A. ureafaciensSD03
*Type species of generic name indicated
References
[BV16] Barka, E. A., P. Vatsa, L. Sanchez, N. Gaveau-Vaillant, C. Jacquard, J. P. Meier-Kolthoff, H.-P. Klenk, C. Clément, Y. Ouhdouch & G. P. van Wezel. 2016. Taxonomy, physiology, and natural products of Actinobacteria. Microbiology and Molecular Biology Reviews 80 (1): 1–43.
Bernasconi, E., C. Valsangiacomo, R. Peduzzi, A. Carota, T. Moccetti & G. Funke. 2004. Arthrobacter woluwensis subacute infective endocarditis: case report and review of the literature. Clinical Infectious Diseases 38: e27–e31.
Busse, H.-J. 2016. Review of the taxonomy of the genus Arthrobacter, emendation of the genus Arthrobacter sensu lato, proposal to reclassify selected species of the genus Arthrobacter in the novel genera Glutamicibacter gen. nov., Paeniglutamicibacter gen. nov., Pseudoglutamicibacter gen. nov., Paenarthrobacter gen. nov. and Pseudarthrobacter gen. nov., and emended description of Arthrobacter roseus. International Journal of Systematic and Evolutionary Microbiology 66: 9–37.
Busse, H.-J., M. Wieser & S. Buczolits. 2012. Genus III. Arthrobacter Conn and Dimmick 1947, 301AL emend. Koch, Schumann and Stackbrandt 1995, 838. In: Goodfellow, M., P. Kämpfer, H.-J. Busse, M. E. Trujillo, K. Suzuki, W. Ludwig & W. B. Whitman (eds) Bergey’s Manual of Systematic Bacteriology 2nd ed. vol. 5. The Actinobacteria, Part A and B pp. 578–624. Springer.
[GM96] Griffiths, A. J. F., J. H. Miller, D. T. Suzuki, R. C. Lewontin & W. M. Gelbart. 1996. An Introduction to Genetic Analysis 6th ed. W. H. Freeman and Company: New York.
[IJSEM02] IJSEM. 2002. Validation list no. 85: Validation of publication of new names and new combinations previously effectively published outside the IJSEM. International Journal of Systematic and Evolutionary Microbiology 52: 685–690.
Mages, I. S., R. Frodl, K. A. Bernard & G. Funke. 2008. Identities of Arthrobacter spp. and Arthrobacter-like bacteria encountered in human clinical specimens. Journal of Clinical Microbiology 46 (9): 2980–2986.
[NC18] Nouioui, I., L. Carro, M. García-López, J. P. Meier-Kolthoff, T. Woyke, N. Kyrpides, C., R. Pukall, H.-P. Klenk, M. Goodfellow & M. Göker. 2018. Genome-based taxonomic classification of the phylum Actinobacteria. Frontiers in Microbiology 9: 2007.
[SD03] Storms, V., L. A. Devriese, R. Coopman, P. Schumann, F. Vyncke & M. Gillis. 2003. Arthrobacter gandavensis sp. nov., for strains of veterinary origin. International Journal of Systematic and Evolutionary Microbiology 53: 1881–1884.
Wauters, G., J. Charlier, M. Janssens & M. Delmée. 2000. Identification of Arthrobacter oxydans, Arthrobacter luteolus sp. nov., and Arthrobacter albus sp. nov., isolated from human clinical specimens. Journal of Clinical Microbiology 38 (6): 2412–2415.