1. Nocard and E.R. Roux (1898)- two French Scientists, discovered these organisms from pleural fluid of cattles suffering from pleuropneumonia. These are pleomorphic and were called PPLO (Pleuropneumonia Like Organisms) or Jokers of plant kingdom. This organism was later on given the name Asterococcus mycoides by Borrel et al. (1910).
Nowak (1929) placed Asterococcus mycoides under the genus Mycoplasma. All such organisms are now called Mycoplasma, or MLO’s (Mollicutes like organisms). These are sometimes placed in a separate class called Mollicuta.
Mycoplasma infects animals (e.g., dog, sheep, mice and man) and plants (e.g., potato, corn, brinjal etc.). they are generally found in soil, sewage water, plants and animals.
These are unicellular , simplest free living prokaryotes. They do not have cell wall so they are highly pleomorphic and can assume various shapes like spherical, granular, filamentous, coccoid etc. Cell membrane is the outermost limiting layer. It is trilamellar unit membrane structure. In culture, colonies of mycoplasma show a characterisitic fried egg appearance with an opaque central area and translucent peripheral zone. The cells are generally non motile, but a few are gliding type. The protoplasmic matrix contains ribosomes (70 S type), fatty substances and proteins. Organized nucleus, endoplasmic reticulum, plastids, mitochondria, golgi bodies, lysosomes, centrioles, flagella, etc. are absent. Mycoplasma has both RNA and DNA. RNA is single stranded , present in both ribosomes and cytoplasm and DNA is double stranded, long coiled thread extending thread extending almost throughout the cell. Enzymes are present freely in the cytoplasm as well as associated with the plasma membrane. Replicating disc assist in replication and separation of the genetic material.
Nature of Mycoplasma :
Mycoplasma can pass though bacteriological filters and lack cell wall. This shows that they are not bacteria. Since they can multiply in abiotic medium having sterols, so they are not considered as virus. Due to many similarities with bacteria they are said to be “Bacteria with their coats off”.
Mode of nutrition is heterotrophic. Some are saprophytic, but mostly they are parasitic. They are parasitic because they are unable to synthesize required growth factors, e.g., M. gallisepticum (0.3 to 0.5 µm, smallest prokaryote). They can survive without oxygen.
Sensitivity to Antibiotics :
Mycoplasma are Gram negative, insensitive to penicillin but sensitive to streptomycin , erythromycin , chloramphenicol ( metabolic inhibitors ) etc., they are insensitive to penicillin because they are wall less and penicillin interferes in the synthesis of peptidoglycan , a component of cell wall of bacteria.
Reproduction – Much is not known about reproduction of Mycoplasma but they mainly reproduce by means of elementary bodies.