Mitchell F. Balish
Assistant Professor of Microbiology
Research Interests:
The long-accepted, simplistic view of the inner workings of the prokaryotic cell has irreversibly changed. Dynamic structures with properties similar to the eukaryotic cytoskeleton have been identified and characterized in many bacteria; these structures are especially important with regard to cell shape, cell division, and subcellular organization. Also, appreciation of bacterial diversity has increased, revealing species that differ considerably from model bacteria. Among these are those bacteria of the class Mollicutes, which are the smallest organisms capable of being grown in pure culture.
Mollicutes, which lack cell walls, have small genomes, and are generally deficient in biosynthetic pathways, are evolutionarily related to the low G+C Gram-positive bacteria. In nature they are associated with animal and plant hosts. The best-studied Mollicutes are those of the genus Mycoplasma (trivial name mycoplasmas), which infect vertebrates, including humans. Of these, the best-characterized is the human pathogen Mycoplasma pneumoniae, which is a leading cause of tracheobronchitis and atypical ("walking") pneumonia, especially in children and young adults. Many other species are significant pathogens of humans and animals, including livestock as well as wildlife creatures.
Although some mycoplasmas are structurally simple, many have prominent polar protrusions called terminal organelles. In some species, these are essential for attachment to host cells (cytadherence) and are called attachment organelles. Attachment organelles are comprised of special cytoskeletal proteins found only in certain mycoplasmas. Other species have terminal organelles that are not directly involved in attachment and whose composition is less certain. Both types of terminal organelle are essential for gliding motility of mycoplasma cells along surfaces, a process whose physiological role appears to be related to host interactions. However, how the components of terminal organelles specifically function in their architecture and virulence-related properties is largely unknown.
In addition to its roles in adherence to host cells and gliding motility, the M. pneumoniae attachment organelle is involved in cell division. Remarkably, in apparent coordination with the onset of DNA replication, the attachment organelle duplicates, and one of the two attachment organelles migrates from one pole of the cell to the other. Following division, the process begins again. The molecular basis for both gliding motility and attachment organelle duplication/migration is almost entirely unknown, not only in M. pneumoniae but also in other mycoplasmas, many of which lack homologs of the known attachment organelle proteins.
The focus of the research in our laboratory is elucidation of the molecular underpinnings of terminal organelle morphology, cell division, cytadherence, and gliding motility in a variety of mycoplasma species. This research carried out through techniques that include time-lapse microcinematographic imaging, fluorescence and electron microscopy, molecular biology, and protein biochemistry.
Current Projects:
- Structure-function relationships in the attachment organelle of M. pneumoniae and its close, human- and animal-associated relatives through the investigation of species with different cytadherence, motility, and morphological properties.
- Contrasting relationships among cytadherence, motility, temperature, and virulence in mycoplasmas with warm-blooded hosts and those with cold-blooded hosts.
- Correlation between attachment organelle duplication and DNA replication in M. pneumoniae.
- Characterization of attachment organelle-associated properties of Mycoplasma penetrans, an organism found in AIDS patients.
- Physiological and molecular studies of mycoplasma morphogenesis.
Selected Publications:
- Relich, R.F., A.J. Friedberg, and M.F. Balish. 2009. Novel cellular organization in a gliding mycoplasma, Mycoplasma insons. J. Bacteriol. 191:5312-5314.
- Atkinson, T.P., M.F. Balish, and K.B. Waites. 2008. Epidemiology, clinical manifestations, pathogenesis and laboratory detection of Mycoplasma pneumoniae infections. FEMS Microbiol. Rev. 32:956-973.
- Hatchel, J.M., and M.F. Balish. 2008. Attachment organelle ultrastructure correlates with phylogeny, not gliding motility properties, in Mycoplasma pneumoniae relatives. Microbiology 154:286-295.
- May, M., G.J. Ortiz, L.D. Wendland, D.S. Rotstein, R.F. Relich, M.F. Balish, and D.R. Brown. 2007. Mycoplasma insons sp. nov., a twisted mycoplasma from green iguanas (Iguana iguana). FEMS Microbiol. Lett. 274:298-303.
- Balish, M.F., and D.C. Krause. 2006. Mycoplasmas: a distinct cytoskeleton for wall-less bacteria. J. Mol. Microbiol. Biotechnol. 11:244-255.
- Hatchel, J.M., R.S. Balish, M.L. Duley, and M.F. Balish. 2006. Ultrastructure and gliding motility of Mycoplasma amphoriforme, a possible human pathogen. Microbiology 152:2181-2189.
- Balish, M.F. 2006. Subcellular structures of mycoplasmas. Front. Biosci. 11:2017-2027.
Faculty: Balish