Mycoplasma

Mycoplasma is a specific genus of bacteria within the class Mollicutes. These organisms are unique because they lack a peptidoglycan cell wall. Most bacteria possess this rigid outer layer to maintain their structure. In Mycoplasma, the plasma membrane serves as the only outer boundary. This absence of a wall makes them naturally resistant to many antibiotics. Specifically, beta-lactam antibiotics work by targeting cell wall synthesis. Since these bacteria have no wall to attack, the medicine fails. This characteristic makes them a significant subject in medical and agricultural science.

The internal structure of Mycoplasma is quite simple compared to other cells. They lack a nucleus and other membrane-bound organelles. Their genetic material consists of a single, naked DNA duplex. They use 70S type ribosomes to build proteins. To help with reproduction, they possess a replicating disc at one end. This disc assists in the replication process and the separation of genetic material. Because they lack a rigid wall, they are pleomorphic. This means they can contort into many shapes, such as round or oblong. They do not follow standard shapes like rods or cocci.

Mycoplasma species follow a unique method of reproduction. In 1954, scientists used phase-contrast microscopy to observe live cells. They discovered that these bacteria do not use binary fission. Binary fission is the standard way most bacteria divide into two equal parts. Instead, Mycoplasma use a uni-polar or multi-polar budding mechanism. This means a new cell grows out from the parent cell like a bud. This discovery helped distinguish them from other types of bacteria. It also helped scientists understand how they survive as such small organisms.

Historically, the classification of these organisms has been very complex. In 1889, Albert Bernhard Frank first used the term "mycoplasma." He was describing changes in plant cytoplasm caused by fungus-like microbes. Later, Julian Nowak used the name for filamentous organisms. These organisms could pass through filters that stopped other bacteria. For a long time, they were called pleuropneumonia-like organisms, or PPLO. This name referred to their similarity to the agent causing bovine pleuropneumonia. Before 1980, some researchers even thought they might be viruses.

Taxonomy, or the science of naming and grouping, has changed significantly. Originally, taxonomists placed them in the phylum Firmicutes. Modern analysis now places them in the phylum Tenericutes. This change happened because they are evolutionarily different from Gram-positive bacteria. In 2018, a scientist named Gupta proposed a major reorganization. He re-circumscribed the genus Mycoplasma around the species M. mycoides. This move removed 78 species from the original genus. This created new families like Mycoplasmoidaceae and Metamycoplasmataceae. While some scientists argued for name stability, a 2022 ruling validated these new names.

These bacteria are highly diverse in their lifestyles and hosts. They can be parasites, commensals, or saprotrophs. Most are parasites that live on plants and animals. They are often heterotrophic, meaning they cannot make their own food. They must take nutrients from a host to grow. This parasitism is often due to their inability to synthesize required growth factors. They are among the smallest free-living organisms, measuring only 0.2 to 0.3 micrometers in diameter. They can be found in humans, animals, and even tortoises.

When grown in a laboratory, Mycoplasma shows very distinct physical traits. If they are grown on Hayflick agar, they form specific colonies. These colonies have a unique "fried egg" appearance. Each individual colony is approximately 0.5 mm in diameter. Studying these colonies helps scientists identify different species. The study of Mycoplasma connects to many fields, including molecular phylogenetics and medicine. Understanding how they evolve and resist drugs is vital for protecting both human and animal health.