Actinobacteria

The Actinobacteria, or Actinomycetota are a group of Gram-positive bacteria. They grow on land or in water. They include some of the most common life forms in soil, playing important roles in the decomposition of organic matter and humus formation. Fungi also play the same role, so some Actinobacteria like Streptomyces were originally classified as fungi. Actinobacteria colonies form branching threads called mycelia. This feature was another reason for the wrongful classification of the actinomycetes, for example, as fungi. 
Some species live in a mutual resource exchange with the roots of plants, such as Frankia, while other species can cause disease, such as the genus Mycobacterium and the bacteria "Mycobacterium tuberculosis."
Actinobacteria contains one of the largest bacterial genera, Streptomyces, which contributes to maintaining the acidity and basicity levels of the soil. They are also important sources of antibiotics, as well as antifungals, antivirals, and numerous other medicines. They are also very useful in agriculture, as they can be used in insecticides and herbicides, among various other substances. Other Actinobacteria species, such as the genus Bifidobacterium, are commonly found in the intestines of infants and are less common in adults.
Some Actinobacteria found in Siberia or Antarctica are considered the oldest on Earth, frozen around half a million years ago.