The members of the Actinobacteria phylum are gram-positive (well mostly) a mix of anaerobic and aerobic and they are one of the largest phyla at this point in time. They are not only the largest group but also have some of the most complex and large cells in the bacterial domain. The members of this phylum all have very different lifestyles and can change their shape accordingly.
Some Actinobacteria live in aquatic environments while others live in the soil or as a part of a plants’ microbiota. they are very good at adapting to their environment. The one member you will have heard of is the Bifidobacterium species as it is in probiotics and frequently talked about in relation to the gut.
The Actinobacteria are a clever bunch so we are using them to produce therapeutic compounds such as antibiotics and other products such as pigments and enzymes that we can use for commercial purposes. They are very important to industries involved in biotechnology, medicine (pharmacy) and agriculture.
Some Actinobacteria can also go bad if given the opportunity. Some of the more notorious members that you may have heard about include Mycobacterium tuberculosis, Corynebacterium diphtheria, Propionibacterium acnes whose names say it all. They love a bit of soft human tissue to burrow into and cause infections which is a bit scary. On a nicer note, these bacteria are found in environmental niches and create that lovely smell after it has rained.
Barka, E. A., Vatsa, P., Sanchez, L., Gaveau-Vaillant, N., Jacquard, C., Klenk, H.-P., . . . van Wezel, G. P. (2016). Taxonomy, Physiology, and Natural Products of <span class="named-content genus-species" id="named-content-1">Actinobacteria</span>. Microbiology and Molecular Biology Reviews, 80(1), 1-43. doi:10.1128/mmbr.00019-15
Puttaswamygowda, G. H., Olakkaran, S., Antony, A., & Kizhakke Purayil, A. (2019). Chapter 22 - Present Status and Future Perspectives of Marine Actinobacterial Metabolites. In V. Buddolla (Ed.), Recent Developments in Applied Microbiology and Biochemistry (pp. 307-319): Academic Press.