Actinomycetota

Beyond the great interest in Actinomycetota for their soil role, much is yet to be learned about them. Although currently understood primarily as soil bacteria, they might be more abundant in fresh waters. Actinomycetota is one of the dominant bacterial phyla and contains one of the largest of bacterial genera: Streptomyces. Streptomyces and other actinomycetota are major contributors to biological buffering of soils. They are also the source of many antibiotics.

Bacteria of the Actinomycetota genus Bifidobacterium are the most common in the microbiome of human infants. Although adults have fewer bifidobacteria, intestinal bifidobacteria help maintain the mucosal barrier and reduce lipopolysaccharides in the intestine.

Although some of the largest and most complex bacterial cells belong to the Actinomycetota, the group of marine Actinomarinales has been described as possessing the smallest free-living prokaryotic cells.

Some Siberian or Antarctic biofilms of these bacteria are said to have the longest lifespan of any organism on Earth, frozen in permafrost at around half a million years ago.

General

Most actinomycetota of medical or economic significance are in class Actinomycetia, and belong to the order Actinomycetales. While many of these cause disease in humans, Streptomyces is notable as a source of antibiotics.

Of those actinomycetota not in the Actinomycetales, Gardnerella is one of the most researched. Classification of Gardnerella is controversial, and MeSH catalogues it as both a Gram-positive and Gram-negative organism.

Actinomycetota, especially Streptomyces spp., are recognized as the producers of many bioactive metabolites that are useful to humans in medicine, such as antibacterials, antifungals, antivirals, antithrombotics, immunomodifiers, antitumor drugs, and enzyme inhibitors; and in agriculture, including insecticides, herbicides, fungicides, and growth-promoting substances for plants and animals. Actinomycetota-derived antibiotics that are important in medicine include aminoglycosides, anthracyclines, chloramphenicol, macrolides, tetracyclines, etc.

Actinomycetota have high guanine and cytosine content in their DNA. The GC content of actinomycetota can be as high as 70%, though some may have a low GC content.

Analysis of glutamine synthetase sequence has been suggested for phylogenetic analysis of the Actinomycetota.