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GENOME SIZE AND LIFE CYCLE OF THE MYCOPLASMA*

Department of Molecular Biophysics and Biochemistry and Department of Microbiology Yale University New Haven, Connecticut 06520
Annals of the New York Academy of Sciences (Impact Factor: 4.31). 12/2006; 225(1):62 - 73. DOI: 10.1111/j.1749-6632.1973.tb45637.x
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    ABSTRACT: Improved methods forstudying thegrowthofMycoplasma hominis(ATCC 14027) havebeendeveloped, involving modified growthconditions andprepara- tion oftheorganisms underminimally distorting conditions. Cells so prepared frombatch cultures showrelatively uniform exponential growthandappear to bedividing bybinary fission; butpleomorphic formsappear upon further incubation. Similar behavior was demonstrated byanother laboratory-adapted strain andbythree clinical isolates, andtherefore seems characteristic ofthe species. Thepleomorphic populations contain smallformshavingdiameters within the100-to250-nmsize range reported for"elementary bodies." Such forms wereisolated fromthis strain ofM.hominis bysequential filtration using gravity alone, after cell aggregates were dispersed byPronase treatment. Ofthe small bodies whichtraversed membranes of220-nm poresize, anegligible num- bergrew inliquid or on solid media, suggesting thatthese were notessential reproductive unitsina life cycle, butinvolution formsduetogrowthin an altered environment. Thebewildering diversity ofevidence and opinion onmycoplasma reproduction (1,9,21) partly reflects fundamental andclearly demon- strable differences between species. However, muchoftheconfusion could havearisen from imperfect understanding oftheirgrowth re- quirements andfromoverlooking their liability tomanipulative distortion. We attempted to determine thetruemorphological changes dur- inggrowth ofareadily cultivable species, Myco- plasma hominis, whencells wereproduced and prepared formicroscopy underoptimal condi- tions. Studies undertaken todetermine amini- mally distorting technique formicroscopy are outlined elsewhere (23).
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