Choose your preferred definition

In a previous post, I've already complained about the undefined definition of the word "actinomycete". Today I might even weep a little.

Using Dictionary.com and Reference.com as sources, I've learnt that an actinomycete can be understood as a bacterium belonging to:

• order Actinomycetales [1,2,3,4], or
  
• phylum Actinobacteria [5,6], or
  
• phylum Chlamydobacteriae, or order Actinomycetales [7], or
  
• genus Actinomyces, or family Actinomycetaceae, or order Actinomycetales [8]

But don't put the blame on dictionary writers. There isn't a unified definition for "actinomycete" since the word lost its status as a class in bacterial nomenclature, long time ago. Anyway, dictionaries are really entertaining, aren't they?

[1] The American Heritage® Dictionary of the English Language, Fourth Edition.
[2] WordNet® 3.0.
[3] Merriam-Webster's Medical Dictionary.
[4] Crystal Reference Encyclopedia.
[5] The American Heritage® Science Dictionary.
[6] Wikipedia, the free encyclopedia.
[7] Dictionary.com Unabridged (v 1.1).
[8] The American Heritage® Stedman's Medical Dictionary.

Definitions retrieved on July 17, 2007, from Dictionary.com website [1,2,3,5,7,8] and from Reference.com website [4,6].

(Dictionary image created at Hetemeel.com. I used a scanning electron micrograph of aerial mycelium and spore of Streptomyces coelicolor; credits: Mark Buttner, Kim Findlay, John Innes Centre)

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Actinomycetes, natural drug factories

Actinomycetes are Gram-positive bacteria with a high GC-content in their DNA. Among others, representative genera include Corynebacterium, Micrococcus, Mycobacterium, Nocardia, Propionibacterium, and Streptomyces. Many actinomycetes, such as Streptomyces, grow as branching filaments and live in soil, as fungi do. Because of this resemblance, actinomycetes were originally classified as fungi. This was reflected on their name, where "mycetes" comes from the Greek for "mushroom, fungus".

Some actinomycetes are pathogenic, such as Mycobacterium tuberculosis. However, many others are extremely useful due to their ability to produce compounds with pharmaceutical properties (antibiotic, antifungal, antitumor, immunosuppressive). The genus Streptomyces is well known precisely for this ability.

In this blog, I intend to post mainly about the biology of actinomycetes, especially those aspects related to the biosynthesis of natural products of pharmaceutical interest. However, I may occasionally deviate from the primary theme. There might be some microbiology, some biochemistry, some chemical biology, some genetics...

Oh, about the title: "Twisted Bacteria". No, it's not that they are "perverted" (although some times we researchers in the field may think so...). The title was inspired by the word "Streptomyces", where "strepto" comes from the Greek for "twisted, twined".

(Image: Streptomyces sp. under the microscope. CDC/Dr. David Berd, Public Health Image Library)

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