Actinobacteria
General information
Description and emendation
This taxon is one of the major phyla in the domain Bacteria, as inferred from its branching pattern in the 16S rRNA gene tree and taxon-specific 16S rRNA signatures. The separation of the phylum from other bacterial taxa is supported by conserved indels in some proteins (e.g., cytochrome-c oxidase subunit 1, CTP synthase and glutamyl-tRNA synthase), by the presence of a large insert in 23S rRNA and by distinctive gene arrangements. The nearest phylogenetic neighbor to the phylum is not clear though the Firmicutes are usually considered in this context. In volume five of the Bergey's Manual, the phylum Actinobacteria encompasses five classes, 19 orders, 50 families, and 221 genera. However, many new taxa continue to be discovered so this listing is inevitably incomplete. The constituent classes are Acidimicrobiia class. nov., Actinobacteria, Coriobacteriia class. nov., Rubrobacteria class. nov., and Thermoleophilia class. nov. Actinobacteria are Gram-stain-positive or Gram-stain-variable aerobes, facultative anaerobes or anaerobes, which have a rigid cell wall that contains muramic acid. Some contain wall teichoic acids. Most are chemo-organotrophs which grow at neutral pH, but some are acidophiles or alkalophiles. Others are halophiles and some are thermophiles. The phylum includes phenotypically diverse organisms which show diverse morphological properties that range from cocci to highly differentiated mycelia. Most are saprophytic, but some are pathogenic for plants and animals. The DNA G+C content ranges from just under 50 mol% (e.g., Hoyosella and Tropheryma) to over 70 mol% (e.g., Frankia and Streptomyces). Members of the taxon are widely distributed in aquatic and terrestrial habitats.