General Microbiology - Schlegel H. 1987

Prokaryotes. Systematic Review
Coryneform bacteria (Group 17)

Corynebacteria. To isolate club-shaped Bacteria (from Greek coryne, meaning club), the genus Corynebacterium was established in 1896, encompassing species similar to the diphtheria bacillus, C. diphtheriae. Besides pleomorphism, a characteristic feature of this genus is Cell "snapping" during division. This occurs because the septum connecting the daughter Cells splits at different rates on opposite sides, causing the cells to suddenly snap at an angle to one another. Alongside this, multiple Cell Division is also observed, whereby a single long rod divides into many short ones. Corynebacterium diphtheriae is the CAUSATIVE AGENT OF diphtheria. Physiologically, this bacterium is an atypical member of the group: it thrives under microaerophilic and anaerobic conditions, whereas most corynebacteria are aerobes. It infects the Pharynx and Tonsils; its pathogenicity is due to the secretion of an exotoxin that circulates in the Blood and affects The Heart Muscle, Kidneys, and nerves ("post-diphtheritic paralysis"). The toxin is produced only under suboptimal cellular iron supply; only lysogenic strains are toxigenic.

The genus Corynebacterium also includes other species, some of which are pathogenic to animals, as well as common plant pathogens (C. michiganense, C. poinsettiae, C. fascians). C. mediolaneum was the first bacterium used for the biological transformation of Steroids (1938).

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Fig. 3.2. Development of an Arthrobacter pyridinolis microcolony on an Agar plate. Numbers indicate incubation time (in hours). Phase contrast. (Kolenbrander P. E., Lotong N., Ensign J. C., Arch. Microbiol., 110 [1976], 239.)

Arthrobacter. The genus Arthrobacter includes several species of coryneform bacteria that are widespread in soil. This genus is characterized by a strong tendency toward cell branching and coccus formation. Some forms are motile due to the presence of flagella. All species are aerobes. Arthrobacter is particularly easily isolated from dry soils; both Arthrobacter and bacilli survive months of dry soil storage, whereas most non-spore-forming bacteria perish. Arthrobacter is pleomorphic—meaning it exhibits morphological diversity—growing as irregularly shaped long rods in young colonies on nutrient media, while older cultures contain coccoid forms (Fig. 3.2). Coryneform soil bacteria also include certain species of Cellulomonas that utilize Cellulose.

Forms grouped within the genus Arthrobacter inhabit diverse environments. Apparently, Arthrobacter is the numerically dominant representative of autochthonous soil microorganisms; that is, it predominates in soils where readily degradable Organic compounds have already been decomposed and humus is the primary remaining fraction of organic matter. Under unfavorable conditions, Arthrobacter is capable of slow growth in the form of cocci. It is likely that the cocci Winogradsky discovered in soils were, in most cases, Arthrobacter cells. Other strains of Arthrobacter are found on plants and in activated sludge from wastewater Treatment plants.

Other genera and species. Many coryneform bacteria excrete glutamic acid (Section 10.2.2) and Other Amino Acids into the medium, which has made them industrially significant. Other forms of these bacteria grow on soft cheeses, such as Brevibacterium linens, possessing moderate proteolytic activity and participating in cheese ripening. More recently, species of Propionibacterium have also been classified among the coryneform bacteria (Section 8.3).

Both morphologically and physiologically, coryneform bacteria occupy an intermediate position between lactic acid bacteria and mycobacteria. The tendency toward branching increases in the progression from propionic acid bacteria and classical corynebacteria to mycobacteria. This progression also reveals a transition from anaerobic to strictly aerobic METABOLISM. However, despite numerous attempts, a clear demarcation between the genera assigned to the coryneform group has not yet been achieved. A new Classification of representatives within this critically important and ecologically diverse group will require data on GC content, murein composition, and other phenotypic traits, as well as numerical Taxonomy data.