Coryneform ​Bacteria
By M Borisova, H Coates, K Durber-Stoneman, E Wilcher
- Arthrobacter sit within the Order of Actinomycetales and the family of Micrococcacae.
- Arthrobacter are Gram-positive, catalase positive bacteria. They are nutritionally versatile and suprisingly resistant to dessication and starvation, given that they are asporogenous (do not form spores). Their developmental cycle involves a transition from rod to coccus and then reversion to rod.The genus is usually considered to contain only obligate aerobes, however, some members of the genus, for example A. globiformis and A. nicotianae , exhibit anaerobic metabolism. (Eschbach, et al., 2003) This adaptation to anaerobic metabolism shows the ability of Arthrobacter species to adapt to changes via diversification.
-Arthrobacter form yellow or white colonies, roughly 2mm in diameter when grown on blood agar. Arthrobacter can also grow on mineral salts pyridone broth. Click the images below for more info regarding Arthrobacter
Arthrobacter
Habitat
-Arthrobacter spp. are most commonly found in soil samples. In terms of ideal temperatures of growth, the genus varies from psychrophilic through to mesophilic, preferring temperatures of 5-30C (Reddy et al., 2000). Arthrobacter are prevalent in many environments, due to their wide growth temperature range, diverse nutritional needs and ability to resist ionizing radiation, oxygen radicals, chemicals and starvation (Mongodin et al.,2006).
Here is a scanning electron microscope image of Arthrobacter globiformis undergoing snapping division, an identifying characteristic of coryneforms.
here is a scanning electron microscope image of Arthrobacter chlorophenolicus, a species able to degrade 4-nitrophenol.
Here is another scanning electron microscope image of Arthrobacter chlorophenolicus, illustrating the morphological differences in arthrobacter, even within the same species.
Here is a scanning electron microscope image of Arthrobacter globiformis undergoing snapping division, an identifying characteristic of coryneforms.
Pathogenicity
-Arthrobacter rarely cause disease, having only been reported five times as the cause of human disease (Bernasconi et al., 2004). However, they have been implicated in isolated cases, such as phlebitis (inflammation of veins) possibly caused by A. albus CF43 (Waters et al., 2000), or scleromata caused by Arthrobacter scleromae (Huang et al., 2005) . The genus' rarity of pathogenicity is evident based on the prevalence of Arthrobacter within soil samples, which humans ubiquitously contact, yet low rates of infection.
Motility
- Unusually for a coryneform ,some species of Arthrobacter exhibit weak flagella dependant motility- e.g. Arthrobacter atrocyaneus. This motility is driven by either peritrichous and subpolar flagella. Peritrichous flagella are found spread evenly across the plasma membrane , whereas subpolar flagellae are found towards the ends of the cell, but not precisely on the poles. An example of each type of flagella can be seen on the left.
Nutritional Requirements
- Arthrobacter can utilise pyridone as their sole carbon source and hence are able to grow on mineral salts pyridone broth, which contains pyridone as its sole carbon source. this ability to metabolize pyridone is an unusual characteristic and a strong factor in identification.
-Species of Arthrobacter have been found which can metabolise 'herbicides, caffeine, nicotine, phenols, and other unusual organic compounds' (Brock et al.,2012). The nutritional diversity which exists within the genus is further outlined below.
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Toxin Neutralisation
-One species, A. crystallopoietes, reduces hexavalent chromium (a carcinogen) to trivalent chromium (much less toxic) in contaminated soil, suggesting that it may be useful in bioremediation. The reason hexavalent chromium can be found in soil is due to its widespread usage in dyes, pigments, refractory material, leather tanning, and electroplating. (Camargo et al, 2004)
-Another species , A. protophormiae , is able to degrade 4-nitrophenol , a pesticide residue and priority pollutant commonly found in soil entirely to form harmless compounds in 5 days. (Labana, et al., 2005)
