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Actinomycetes are classified into 7 families. The classification is based on hyphal and reproductive structures.
Family 1:
Streptomycetaceae:
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Hyphae non-fragmented, aerial mycelium with chains of spores with 5 to 50 or more conidia per chain e.g. Streptomyces, Microdlobaspone and Sporictilhya.
Family 2:
Nocardiaceae:
Hyphae typically fragmented e.g. Nocardia, Pseudonocardia.
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Family 3:
Micromononsporaceae:
Hyphae non-fragmented conidia borne singly or in pairs or in short chains, e.g. Micromonospora, Thermonospora, Thermoactinomycetes, Actinobifida.
Family 4:
Actinoplanaceae:
Sporangia bear the spores. The hyphal diameter varies from 0.2 to 2.0 µm e.g. Streptosporangium, Actinoplanes, Plasmobispora and Dactylosporangium.
Family 5:
Dermatophilaceae:
Hyphal fragments divide to form large numbers of round, motile structures e.g. Geodermatophilus.
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Family 6:
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Frankiaceae:
It is strictly associated with root of non-leguminous plant and form root nodules e.g. Frankia.
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Family 7:
Actinomycetaceae:
No true myceluim is produced, usually strictly to facultative anaerobic e.g. Actinomyces.
Due to the development of modem techniques of molecular biology such as 16S rRNA sequencing, phylogeny and relationship, mycelium has the following criteria.
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The actinomycetes lines of descent (including the Atopobium, Sphaerobacter and the lineages) includes the following:
(a) The Actinomycete, Bifidobacterium, Arthrobacter and Relatives
(b) The family actinomycetaceae and relatives, Propionibacterium and relatives
The mycolic acid containing genera (formerly the CMN Cluster)
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(c) The family Actinoplanaceae and relatives.
(d) The family Pseudonocardiaceae and relatives.
(e) The family Frankiaceae and relatives.
(f) The family Streptomycetaceae and Streptosporangiaceae and the genera Actinomadura and Nocardiopsis.
(g) Actinomycetes of uncertain phylogenetic applications.
