PPLO-The Pleropnemonia-like Organisms
⦿ The pleuropneumonia-like organisms or PPLO are the bacteria-. like organisms which differ with the latter only in lacking the cell wall and mesosomes and in having very simple organization, small sİze and a deformable cytoplasmic or plasma membrane around their prokaryotic cells.
⦿ W. V. Iterson (1969) has placed PPLO in the group Mycoplasmataceae of bacteria (Schizomycetes), but, Novikoff and Holtzman (1970) have considered them as simplest known cells and have excluded themn from the bacteria.
⦿ The diameters of the Smallest PPLO are 0-1 03um, and of the largest on the order of a micron. Thus, in size, the PPLOs overlap with the largest viruses and with the smallest bacteria.
⦿ The most widely studied genus of PPLO is Mycoplasma.
⦿ The Mycoplasmas are the smallest organisms that have been cultivated on cell-free media.
⦿ Two types of Mycoplasmas exist in the nature.
⦿ The first with Mycoplasma laidlawii (0-1 m diameter) as the m type species, is saprophytic.
⦿ It is found in sewage, compost, earth, etc.
⦿ The second type with Mycoplasma galisepticum as the type species, is parasite of the cells and cell /exudates of respiratory organs of warm-blobded animalş.
⦿ It causes various chronic respiratory diseases in them.
Structure
⦿ The prokaryotic yells of PPLO remain bounded by a 75A° thick plasma menmbrane.
⦿ The DNÀ molecue is contained in a nuclear region.
⦿ DNA molecule may be in the form of either ibrils or a single circluar double helix and it is not enveloped by any nuclear membrane.
⦿ The nuclear region is surrounded by numnerous ribosomes and other components involved in protein synthesis.
⦿ The cytoplasm has some granules and vacuoles of uncertain significance. .
⦿ The vacuoles are said to be formed due to deep infoldings of the plasma membrane
⦿ At one side of the cell occurs bleb of ill under- stood function.