(Speaker Term: 7/1/12 - 6/30/14)
Department of Biology, Box 1137
1 Brookings Drive
St. Louis, MO 63130
LECTURE TOPICS AND DESCRIPTIONS
Spatial and Temporal Mechanisms Governing Bacterial Cell Division
In all organisms, precise temporal and spatial controls coordinate cell division with cell growth, DNA replication, and chromosome segregation to ensure that genetic and cytoplasmic material is properly distributed between daughter cells. In bacteria, the location of the division site is determined by the essential cell division protein FtsZ. Work from our lab and others indicate that the spatial and temporal control of cell division is achieved through the concerted actions of many factors on FtsZ assembly dynamics. The impact of a handful of these regulators on the temporal and spatial control of cell division in Bacillus subtilis will be discussed.
Carbon Sensing and Cell Size
The model bacteria Escherichia coli and Bacillus subtilis increase cell size in response to increases in carbon availability. During growth in carbon rich medium, both organisms are approximately twice the size of their counterparts cultured in carbon poor medium. The increase in size is required to ensure that cells are large enough to accommodate the extra DNA generated by multifork replication. We have identified the signal transduction pathways responsible for sensing carbon availability and transmitting this information to the division apparatus in both organisms, and we are now focused on characterizing them at the molecular level.
Cell Size and Cell Cycle Progression in Bacteria
DNA replication must be coupled to growth and division to ensure that daughter cells are of sufficient size and inherit complete genomes. In bacteria, data primarily from Escherichia coli suggests that growth dependent accumulation of the highly conserved initiator, DnaA, triggers replication initiation. However, the timing of initiation is unchanged in Bacillus subtilis mutants that are ~30% smaller than wild type cells, suggesting achievement of a particular cell size is not obligatory. We have re-examined the link between cell size and initiation in both E. coli and B. subtilis. We find that although DnaA is almost certainly required for initiation in all bacteria, the mechanisms governing its activity can be distinct in different bacteria.
BIOGRAPHICAL SKETCH - Petra Anne Levin
Cell division must be coordinated with cell growth, DNA replication, and chromosome segregation to ensure that daughter cells are the appropriate size and that genetic material is properly distributed. To develop a comprehensive picture of how division is regulated in time and space, my lab has sought to identify and characterize factors controlling cell division in two model bacteria, Bacillus subtilis and Escherichia coli. In bacteria, the essential cell division protein, FtsZ, assembles into a ring structure that establishes the location of the division site. To date, all of the regulators we have identified impact FtsZ in some manner, either by inhibiting FtsZ assembly at aberrant subcellular positions, increasing turnover of FtsZ at the division site, or by coordinating FtsZ ring formation with cell growth. Notably, we are the first to identify the means by which bacterial cells coordinate cell size with nutrient availability, answering a long-standing question in bacterial physiology. Together, our findings support a model in which the spatial and temporal control of bacterial cell division is achieved through the concerted actions of many factors on FtsZ assembly.
Dr. Levin's CV is available on her website: http://www.biology.wustl.edu/levin/
ASM MEMBERSHIP AFFILIATION - Petra Anne Levin
Primary Division: H (Genetics & Molecular Biology)
Secondary Division: K (Microbial Physiology & Metabolism)