Plasmid copy number noise in monoclonal populations of bacteria

Author(s): Jérôme Wong Ng, Didier Chatenay, Jérôme Robert, Michael Guy Poirier

Abstract:

“Plasmids are extra chromosomal DNA that can confer to their hosts’ supplementary characteristics such as antibiotic resistance. Plasmids code for their copy number through their own replication frequency. Even though the biochemical networks underlying the plasmid copy number (PCN) regulation processes have been studied and modeled, no measurement of the heterogeneity in PCN within a whole population has been done. We have developed a fluorescent-based measurement system, which enables determination of the mean and noise in PCN within a monoclonal population of bacteria. Two different fluorescent protein reporters were inserted: one on the chromosome and the other on the plasmid. The fluorescence of these bacteria was measured with a microfluidic flow cytometry device. We show that our measurements are consistent with known plasmid characteristics. We find that the partitioning system lowers the PCN mean and standard deviation. Finally, bacterial populations were allowed to grow without selective pressure. In this case, we were able to determine the plasmid loss rate and growth inhibition effect.”

Link to Publications Page

Publication: Physical Review E
Issue/Year: Phys. Rev. E, Volume 81, Issue 1, 011909 (2010)
DOI: 10.1103/PhysRevE.81.011909

Nonspherical laser-induced cavitation bubbles

Author(s): Kang Yuan Lim, Pedro A. Quinto-Su, Evert Klaseboer, Boo Cheong Khoo, Vasan Venugopalan, Claus-Dieter Ohl

Abstract:

“The generation of arbitrarily shaped nonspherical laser-induced cavitation bubbles is demonstrated with a optical technique. The nonspherical bubbles are formed using laser intensity patterns shaped by a spatial light modulator using linear absorption inside a liquid gap with a thickness of 40 μm. In particular we demonstrate the dynamics of elliptic, toroidal, square, and V-shaped bubbles. The bubble dynamics is recorded with a high-speed camera at framing rates of up to 300 000 frames per second. The observed bubble evolution is compared to predictions from an axisymmetric boundary element simulation which provides good qualitative agreement. Interesting dynamic features that are observed in both the experiment and simulation include the inversion of the major and minor axis for elliptical bubbles, the rotation of the shape for square bubbles, and the formation of a unidirectional jet for V-shaped bubbles. Further we demonstrate that specific bubble shapes can either be formed directly through the intensity distribution of a single laser focus, or indirectly using secondary bubbles that either confine the central bubble or coalesce with the main bubble. The former approach provides the ability to generate in principle any complex bubble geometry.”

Link to Publications Page

Publication: Physical Review E
Issue/Year: Phys. Rev. E, Volume 81, Issue 1, 016308 (2010)
DOI: 10.1103/PhysRevE.81.016308