#actinomycetota

[bacteriashowdown]

Actinomycetota vs. Thermomicrobiota

Actinomycetota propaganda here

Thermomicrobiota propaganda here

Actinomycetota vs. Thermomicrobiota

Actinomycetota

Thermomicrobiota

Voting ended onMar 8, 2024

[bacteriashowdown]

Actinomycetota

Group: Terrabacteria

Gram-stain: Positive

Etymology: For Actinomyces bovis. From the Greek "aktis", meaning "ray", and "myketes", meaning "fungus". Some bacteria in this phylum form fungus-like branched colonies, hence the name: "ray fungus". Note the similarity to mycelium networks.

About: Actinomycetota contains tuberculosis (Mycobacterium tuberculosis), the leading cause of death by bacterial infection. It is also the second leading cause of death by any infectious disease, only surpassed by COVID-19. Many other members of the genus Mycobacterium are also pathogenic, such as Mycobacterium leprae, which is responsible for Hansen's disease (better known as leprosy).

But Actinomycetota is far from all bad. In fact, it is possibly the most studied and used bacterial phylum in terms of medical, agricultural, environmental, and biotechnological applications. Actinomycetota play a huge role in nutrient cycling in soil ecosystems, making them crucial for maintaining the health of soil. They are therefore a pillar of modern agriculture. Some Actinomycetota are nitrogen-fixing, and can be symbiotic with trees. The phylum is also a source of antibiotics, especially with the genus Streptomyces: these bacteria naturally produce several antimicrobials (including streptomycin), and thus have use both in medicine and as a natural pesticide against other microorganisms in the soil.

Actinomycetota colonies have long been noted to resemble those of fungi, and early researchers originally believed that this phylum was a fungi. Indeed, Actinomycetota and fungi share similar roles, being largely decomposers. However, the much smaller Actinomycetota fill their own ecological niche.

In terms of reproduction, Actinomycetota and fungi are especially similar. Actinomycetota produce spores, but not just endospores: they also form spores using external structures called "hyphae". Hyphae are branched, filamentous structures that make up what is called a "mycelium", and can have a variety of shapes. Many hyphae, including those in Actinomycetota, are reproductive structures that subdivide to create spores. This is a process ubiquitous among fungi but limited to pretty much only the Actinomycetota phylum of bacteria. The below image depicts some possible hyphae structures in Streptomyces bacteria: 

In addition to all this, Actinomycetota may contain the oldest living organisms on earth, which could have been frozen in Siberian or Antarctic ice for thousands (or millions) of years. While Actinomycetota do produce durable endospores, it is also theorized that they may also be able to survive in a frozen but non-dormant state: not reproducing, but still metabolizing, and thus being able to repair their DNA.

While the theory is speculative, evidence of metabolic activity has been detected from soil samples after more than 600,000 years of permafrost, studied under ambient conditions (i.e. not thawed to trigger endospore germination). We have actually cultivated Actinomycetota from other ancient permafrost samples, such as 28,000 year old mammoth poop.