Structure and Function of the Electron-dense Core in Mycoplasma pneumoniae and its Relatives
Among the mycoplasmas, the human pathogen Mycoplasma pneumoniae is the best-characterized at the cellular level. It has a polar structure, the attachment organelle, which mediates adherence to host cells, is the leading end during gliding motility, and plays a role during cell division. Within the attachment organelle is a detergent-insoluble electron-dense core composed of several proteins, some of which have been identified through the study of cytadherence deficient mutants of M. pneumoniae. Mutants lacking proteins in the electron-dense core are avirulent, suggesting that the core is essential for the proper formation of the attachment organelle, which in turn is essential for virulence. We used scanning electron microscopy (SEM) and time-lapse microcinematography to test the relationship between ultrastructure and gliding motility in M. pneumoniae and some of its close phylogenetic relatives, which vary in ultrastructure, gliding characteristics, host range, and pathogenic potential. Our results show that Mycoplasma amphoriforme, a novel species found in the respiratory tract that is possibly pathogenic to humans, is motile and shares morphological characteristics with its closest relatives, M. pneumoniae and the avian pathogen, Mycoplasma gallisepticum. Using SEM and time-lapse microcinematography, we find that the morphology of seven species of the M. pneumoniae cluster correlates with phylogeny rather than with gliding motility characteristics. We also find that in most species the electron-dense cores have fibers and filaments that remain attached to the base of the core after detergent treatment, but disappear after treatment with DNase, suggesting that they are DNA. It has been hypothesized that the electron-dense core plays a role during cell division, which might utilize protein-DNA interactions between the core and the chromosome. Using fluorescence in situ hybridization (FISH) coupled to immunofluorescence, we attempted to further investigate specific interactions between the oriC region of the chromosome and the electron-dense core in M. pneumoniae. The data suggest that a variable region of the chromosome associates with the base of the electron-dense core, although the FISH protocol still needs optimization. Overall, my work suggests that gliding motility has a major role in the partitioning of the chromosomes in cell division and a minor role in pathogenicity.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:mycoplasma pneumoniae gliding motility cell division attachment organelle morphology
Date of Publication:07/22/2009