Events at Physics |
Events on Tuesday, November 24th, 2009
- Chaos & Complex Systems Seminar
- Directed evolution of ionizing radiation resistance in Escherichia coli
- Time: 12:05 pm
- Place: 4274 Chamberlin (Refreshments will be served)
- Speaker: Michael Cox, UW Department of Biochemistry
- Abstract: We have generated extreme ionizing radiation resistance in a relatively sensitive bacterial species, Escherichia coli, by directed evolution. Four populations of Escherichia coli K12 were independently derived from strain MG1655, each specifically adapted to survive exposure to high doses of ionizing radiation. D37 values for strains isolated from two of the populations approached that exhibited by Deinococcus radiodurans. Complete genomic sequencing was carried out on nine purified strains derived from these populations. Clear mutational patterns were observed that both pointed to key underlying mechanisms and guided further characterization of the strains. In these evolved populations, passive genomic protection is not in evidence. Instead, enhanced recombinational DNA repair makes a prominent but probably not exclusive contribution to genome reconstitution. Multiple genes, multiple alleles of some genes, multiple mechanisms, and multiple evolutionary pathways all play a role in the evolutionary acquisition of extreme radiation resistance. Several mutations in the recA gene and a deletion of the e14 prophage both demonstrably contribute to and partially explain the new phenotype. Mutations in additional components of the bacterial recombinational repair system and the replication restart primosome are also prominent, as are mutations in genes involved in cell division, protein turnover and glutamate transport. At least some evolutionary pathways to extreme radiation resistance are constrained by the temporally ordered appearance of specific alleles.
- Astronomy Colloquium
- The Evolution of Red Galaxies in Clusters Over Half of Cosmic Time
- Time: 3:30 pm - 5:00 pm
- Place: 3425 Sterling Hall
- Speaker: Dr. Greg Rudnick, University of Kansas
- Abstract: Tracking the growth of stellar mass in galaxies is a fundamental characterization of the galaxy population. Recent observations have shown that the total mass in L>L* red galaxies has increased by a factor of ~2 at z<1, although at different rates as a function of galaxy mass. Despite the advance made by these studies of the whole galaxy population, until recently it has not been clear if the growth of the red sequence depended on environment. Galaxy clusters are a useful probe of this as they sample the most extreme environments. However, progress toward answering this question has been hampered by a lack of deep multi-band imaging of a large sample of clusters that can be well linked to those in the local universe. To address this I will present the evolution of the red sequence as measured in 16 intermediate redshift clusters drawn from the ESO Distant Cluster Survey (EDisCS). Unlike massive x-ray selected clusters, these clusters have velocity dispersions that make them likely progenitors of clusters that populate the local Universe. I will show how the luminosity function (LF) of red-sequence galaxies in these clusters has evolved over 50% of cosmic time, highlighting the rapid buildup of the faint cluster galaxy population. I will also compare the evolution of the red sequence in clusters to the evolution of the field red sequence population and show that they evolve at different rates. Finally I will address how the total mass on the red sequence evolves in clusters and will use this to constrain the mechanisms of how red galaxies can be added to clusters. From this analysis it appears likely that some fraction of the light in recently added cluster red sequence galaxies is currently in the in the form of intracluster stars.
- Host: Professor Christi Tremonti
- String Theory Seminar
- Stanford Holographic Lattices, Dimers, and Glasses
- Time: 4:00 pm
- Place: 2301 Sterling Hall
- Speaker: Sho Yaida, Stanford University
- Host: Gary Shiu