Higher order taxa
Bacteria; Actinobacteria; Actinobacteria; Actinobacteridae; Actinomycetales; Micrococcineae; Micrococcaceae 
Description and significance
Bacteria of the genus Arthrobacters are typically found in soil, but are widely distributed in the environment. Arthrobacter globiformis is one of the species that is found in soil. Arthrobacter means “jointed small stick” in Greek. All Artrhobacter species are rods during growth and cocci in their stationary phase. Also, all Arthrobacter species are gram-positive, but A. globifomris is gram-negative during exponential growth and gram-positive in its stationary phase. American bacteriologists, Harold J. Conn and Isabel Dimmick, introduced the genus name Arthrobacter in 1947 reviving it from a hypothetical name that was proposed by German botanist, Alfred Fischer. Conn and Dimmick classified three species in the genus Arthrobacter, and one of the species was A. globiformis. Now there are 64 species within the genus Arthrobacter.
A. globiformis is nonmotile. Its colonies on yeast media have no distinctive pigmentation (5). Colonies of A. globiformis that has been grown on nutrient agar is smooth, circular, convex eleveation with entire margin. Most strains from the genus Arthrobacter appear to be nonpathogenic to humans and nonsporulating. Arthrobacter is distinctive because of its unique cell division known as “snapping division.” Snapping division occurs because there are two cell wall layers and the inner layer forms a septum while the outer layer does not. When the septum formation is complete, the outer layer keeps them from being attached. Eventually, the outer wall ruptures at a joint (1).
Genome and genetics
Arthrobacter have a close phylogenetic relationship with the genus Corynebacterium. A. globiformis has a 97.6% 16S rRNA gene similarity with the species Arthrobacter crystallopoietes. When the 16S rRNA sequence of Arthrobacter russicus is compared to A. globiformis, A. russicus has a 12-bp insertion, which is also found in Rhenibacterium salmonarum and other related Arthrobacter species (5). A. globiformis is one of the species of Arthrobacter that has a complete genome sequence available. Its genome was sequenced using whole genome shotgun sequencing (2). The genome analysis showed that the soil isolates have many genes encoding stress-related protein (7). The A. globiformis and A. citreus group differs from the A. nicotianae group by their lipid composition, teichoic acid, and peptidoglycan structure. The strain FB24 is a part of the A. globiformis/ A. citreus group indicated by the 16 rRNA gene sequence. The closest sequence of strain FB24 is from A. globiformis with a 98% similarity(6).A. globiformis grows to 4.95 Mb in size (1).
Nutrition and metabolism
A. globiformis uses ammonium salt or nitrate as a sole nitrogen source and glucose as a carbon and energy source. Arthrobacter species are obligate aerobes, but remarkably, A. globiformis is one of the two species of Arthrobacter that showed the ability of anaerobic respiration without nitrite, using nitrate, glucose and pyruvate as carbon sources. (5).
The age of the media seems to be important in the morphology of Arthrobacter. In “young” culture, the bacteria is rod-like whereas in "older" culture, the bacteria is coccoid. The optimal growth temperature for the Arthrobacter species is between 20-30°C. They also prefer a neutral to slightly alkaline pH for growth.
Members of the genusArthrobacter were first found in the soil in the 19th century. Since then, they have shown to be metabolically resourceful as they can grow on a variety of substrates. A. globiformis has a significant positive role in its environment in many ways. It has the ability to oxidize ammonium into nitrite, nitrate and hydrylamine. This is important because A. globiformis provides reliable source of nitrogen that plants need to grow. A. globiformis can also reduce pesticides as well as other harmful chemicals that are found in the soil. A lot of plants are not capable of growing in the presence of hexavalent and trivalent chromium, but A. globiformis can do so, and can even help reduce the amount of trivalent chromium (3). Due to their metabolic diversity, Arthrobacter species have been used to biodegrade diverse types of pollutants in our environment (1).
In the research paper, “Increased iron-stress resilience of maize through inoculation of siderophore-producing Arthrobacter globiformis from mine,” wheat and maize were inoculated with A. globiformisto increase iron-stress resilience. Iron deficiency is common among these and other graminaceous crops. Plants from iron-limiting habitats most likely have a bacterium that secrete iron-chelating molecules to mobilize and solubilize iron. A. globiformis dissolves diverse iron complexes effectively and its siderophores have a high iron chelation capacity (8).
In 2014, a research was conducted on A. globiformis, exposing it to silver nanoparticles. Silver nanoparticles are widely used because of their antimicrobial properties. Due to their increasing use in consumer products, silver nanoparticles are sure to find their way into the environment. The results of this study showed that soils with silver nanoparticles had a concentration-dependent reduction of Arthrobacter dehydrogenase activity (4).
1. Arthrobacter - Details. Encyclopedia of Life. [accessed 2017 Mar 30]. http://eol.org/pages/97262/details
2. Arthrobacter globiformis (ID 12154). National Center for Biotechnology Information. [accessed 2017 Mar 31]. https://www.ncbi.nlm.nih.gov/genome/?term=Arthrobacter globiformis
3.Combined-Notes. Arthrobacteria globiformis/Combined-notes. [accessed 2017 Mar 29]. http://meaghanemma.pbworks.com/w/page/10520223/Combined-Notes.
4. Engelke M, Köser J, Hackmann S, Zhang H, Mädler L, Filser J. A miniaturized solid contact test with Arthrobacter globiformis for the assessment of the environmental impact of silver nanoparticles. Environmental toxicology and chemistry. 2014 May [accessed 2017 Mar 30]. https://www.ncbi.nlm.nih.gov/pubmed/24477989
6. Home - Arthrobacter sp. FB24. DOE Joint Genome Institute - JGI Genome Portal. [accessed 2017 Mar 31]. http://genome.jgi.doe.gov/art_f/art_f.home.html
7. Niewerth H, Schuldes J, Parschat K, Kiefer P, Vorholt JA, Daniel R, Fetzner S. Complete genome sequence and metabolic potential of the quinaldine-degrading bacterium Arthrobacter sp. Rue61a. BMC Genomics. 2012 Oct 6 [accessed 2017 Mar 30]. http://bmcgenomics.biomedcentral.com/articles/10.1186/1471-2164-13-534
8.Sharma M, Mishra V, Rau N, Sharma RS. Increased iron-stress resilience of maize through inoculation of siderophore-producing Arthrobacter globiformis from mine. Journal of basic microbiology. 2016 Jul [accessed 2017 Mar 30]. https://www.ncbi.nlm.nih.gov/pubmed/26632776