Filamentous Actinomycetes

 

Filamentous Actinomycetes is a morphologically named group encompassing eight key genera; Actinomyces, Mycobacteria, Nitrogen-fixing Actinomyces, Actinoplanes, Dermatophilus, Nocardias, Streptomyces, and Micromonosporas.

The Filamentous Actinomycetes are considered the classical link between bacteria and fungi. These bacteria behave similarly to Fungi but form filaments for a variety of reasons. There are distinct differences between genera but they all share aerobic, Gram-positive characteristics.

 

First records of an actinomycete-like species were of Streptothrix foersteri by Cohn in 1875, found in a human tear duct, although it has since been identified as a fungus. In 1877 Actinomyces bovis was identified by Harz as a pathogen which causes lumpy jaw in cattle.

 

The majority of the genera have a high G:C ratio, a feature not commonly seen in gram positive bacteria. The characteristic filaments form a highly dense network called a mycelium, depending on genera this can differentiate into a spore forming aerial mycelium upon maturation. This feature initially led to an incorrect classification as fungi, however fungi have thicker hyphae. This along with new, more sophisticated taxonomical methods led to the ability to identify them as bacteria.

 

More than half of the genera are soil based organisms, there are also those that exist in water, on humans, and as obligate plant symbionts.

 

 

References:

Madigan, M., Martinko, J., Stahl, D. and Clark, D. (2012). Brock biology of microorganisms. 13th ed. San Francisco, Calif.: Pearson.

Mishra, S. and Agrawal, D. (2012). A concise manual of pathogenic microbiology. Hoboken, N.J.: Wiley-Blackwell.

Waksman, S. (1959). The Actinomycetes; Nature, Occurrence and Activities. London: Bailliere, Tindall & Cox, ltd.

Mycobank.org, (2014). Streptothrix foersteri. [online] Available at: http://www.mycobank.org/Biolomics.aspx?Table=Mycobank&MycoBankNr_=247272 [Accessed 27 Oct. 2014].

Paul Singleton, Diana Sainsbury, (2001) Dictionary of Microbiology

Molecular Biology, Third edition revised, London , John Wiley & Sons Ltd page 8-9

Mincer, T., Jensen, P., Kauffman, C. and Fenical, W. (2002). Widespread and Persistent Populations of a Major New Marine      Actinomycete Taxon in Ocean Sediments. APPLIED AND ENVIRONMENTAL MICROBIOLOGY, 68(10), pp.5005-5011.

Whitman, W., Parte, A., Goodfellow, M., Kämpfer, P., Busse, H., Trujillo, M., Ludwig, W. and Suzuki, K. (2012). Bergey's Manual of  Systematic Bacteriology. New York: Springer.