Other Mycoplasma sp.

Abstract

Mycoplasmas are members of a genus belonging to the class Mollicutes (soft skin). Classic properties which distinguish the genus are their rigid sterol-containing membrane and complete lack of cell wall components (Razin, 1985). Currently they are recognized as having the smallest and simplest genomes of all free living-species (Krawiec and Riley, 1990; see Chapters 1 and 37). Although capable of being cultivated as free-living organisms in the laboratory when their extremely fastidious nutritional requirements are met, virtually every species exists in nature in a parasitic or saprophytic relationship with some specific higher eukaryotic plant, animal or insect (Razin and Jacobs, 1992). Species were originally defined and differentiated serologically from differences in surface exposed antigens and although host specific, the parasitic associations were thought to be exclusively extracellular. With the advent of molecular hybridization and PCR as diagnostic or detection techniques there is increasing evidence that some species might be capable of intracellular associations as well (Whitcomb et al., 1995; Krause and Taylor-Robinson, 1992; Mernaugh et al., 1993; Taylor-Robinson et al., 1991). Hence, significance of the pathogenic potential of Mycoplasmas, especially in mammalian systems, is being reevaluated. Since individual cells are pleomorphic, often filamentous, and difficult to cultivate by conventional clonal techniques on solid media, classic genetic analysis has been very slow to develop. Although genetic transformations, including transposon insertions have been described in this group (Dybvig and Alderete, 1988; Hedreyda et al., 1993; King and Dybvig, 1994; Whitley and Finch, 1989; Cao et al., 1994; Kapke et al., 1994), the fastidiousness of species precludes the isolation of conventional auxotrophs. There has also not been a systematic use of those gene manipulation procedures to derive large collections of mutant loci “markers,” or to establish genetic map distances by recombination analyses among mutants.