title: Monitoring microbial population dynamics at low densities.
abstract: We propose a new and simple method for the measurement of microbial concentrations in highly diluted cultures. This method is based on an analysis of the intensity fluctuations of light scattered by microbial cells under laser illumination. Two possible measurement strategies are identified and compared using simulations and measurements of the concentration of gold nanoparticles. Based on this comparison, we show that the concentration of Escherichia coli and Saccharomyces cerevisiae cultures can be easily measured in situ across a concentration range that spans five orders of magnitude. The lowest measurable concentration is three orders of magnitude (1000×) smaller than in current optical density measurements. We show further that this method can also be used to measure the concentration of fluorescent microbial cells. In practice, this new method is well suited to monitor the dynamics of population growth at early colonization of a liquid culture medium. The dynamic data thus obtained are particularly relevant for microbial ecology studies.
authors.affiliation: Laboratoire de Physique Statistique de l'École Normale Supérieure, UMR8550, associé au CNRS et aux Universités Paris VI et Paris VII, 24 rue Lhomond, 75005 Paris, France. thomas.julou@normalesup.org
authors.forename: Thomas
authors.initials: T
authors.lastname: Julou
authors.forename: Nicolas
authors.initials: N
authors.lastname: Desprat
authors.forename: David
authors.initials: D
authors.lastname: Bensimon
authors.forename: Vincent
authors.initials: V
authors.lastname: Croquette
mesh_terms: D002452:Cell Count; D015169:Colony Count, Microbial / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007834:Lasers; D008029:Lighting / Q000295:instrumentation*; D010783:Photometry / Q000295:instrumentation*; D013057:Spectrum Analysis / Q000295:instrumentation*