1. IDENTIFYING
CHARACTERISTICS
Arthrobacter exhibit rod morphology during their exponential growth phase (bar = 10um).
2. TAXONOMIC
DESCRIPTION
There are approximately 15 species of the genus Arthrobacter. These are divided into two groups based on variations in peptidoglycan and menaquinone content. A. globiformis is the type species (ATCC 8010). Arthrobacter are chemoorganotrophs exhibiting only respiratory metabolism, never fermentative. Little acid is produced when grown on glucose in peptone media. Growth is optimum in neutral to slightly acidic environments. Arthrobacter are able to hydrolyze gelatin but not cellulose, and most require biotin as the only specific growth facter. Their nutrional versilatility allows them to use a range of carbon sources including such things as; uric acid, caffeine, herbicides, and nicotine. For these reasons, Arthrobacter are extremely competitive organisms with remarkable resistance to dessication and starvation.
Arthrobacter exhibit coccoid morphology during their stationary growth phase (bar = 10um).
3. ISOLATION AND ECOLOGY
The unique life cycle of Arthrobacter is useful for it's isolation. A soil suspension is plated onto a relatively poor growth media and incubated for a short period of time. Transfer of coccoid cells to a rich agar causes the cells to swell and produce rod outgrowths. Over a period of time, the rods shorthen to become cocci upon reaching the stationary growth phase. Selective media are also available for isolation. Colonies grow to 3-5 mm in diameter and are usually cream or buff in color, some are faint shades of yellow.
Ubiquitous in soil, Arthrobacter may account for 5-60% of total bacterial counts. Their presence decreases with increasing soil acidity. Several species have been found in subterranean caves, sediments, and sewage. A. globiformis forms a symbiotic relationship with Anabaena (a nitrogen fixing cyanobacteria) and Azolla (an aquatic fern). This Arthrobacter species produces a mucilagenous substance which enhances the infection of the fern by the cyanobacteria. The optimum growth temperature of most species is 25-30 C. However, some psychrotropic stains have developed cold shock and cold acclimation protens allowing them to sustain life at low temperatures. Some species of Arthrobacter are found in saline and/or water deficient environments. For example, A. globiformis uses choline oxidase to prevent the denaturation of soluble enzymes at high salt concentrations. Current research includes molecular techniques designed to isolate choline oxidase and insert it into cyanobacteria and higher plants as a means of improving their salt tolerance. Other research explores the use of Arthrobacter to remediate subsurface pollution. The ubiquitous nature of Arthrobacter coupled with their ability to degrade herbicides like glyphosate (N-phosphomethyl-glycine) and pentachlorophenols (PCPs), suggests that they could become useful in environmental cleanup.
4. ADDITIONAL SOURCES OF INFORMATION
Atlas, R.M. 1993. Handbook of Microbiological Media. CRC Press. Boca Raton, Florida. 1079 pp.
Conn, H.J. and Dimmick. 1947. Soil bacteria similar in morphology to Mycobacteriumand Corynebacterium. J. Bacteriol. 54: 291-303.
Hagedorn, C. and J.G. Holt. 1975. A nutritional and taxonomic survey of Arthrobacter soil isolates. Can. J. Microbiol. 21: 353-361.
Holt, J.G., N.R. Krieg, P.H.A. Sneath, J.T. Staley, and S.T. Williams. 1994. Bergey's Manual of Determinative Bacteriology. Ninth Edition. Williams and Wilkins. Baltimore, Maryland. 787 pp.
5. LINKS TO OTHER SITES ON Arthrobacter:
http://www.gbf-braunschweig.de/DSMZ/dsmzhome.htm
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