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Non-invasive Measurement of the Population Density of E. coli Grown in Simulated Microgravity.  J.M. Manley1, M.R. Benoit2 and D.M. Klaus2.  1Dept of Environmental Populational and Organismic Biology, 2Dept of Aerospace Engineering Sciences, University of Colorado at Boulder.

  Space flight has been shown to alter bacterial cell growth kinetics resulting in changes such as increased final cell population density and shortened lag phase duration.  A clinostat is often used to study the effects of space flight in a 1 g environment and typically leads to similar trends.  Collecting samples to determine final cell population density is relatively straightforward, but doing so throughout the cell growth period disrupts the desired environmental conditions (whether the 1g controls, in space, or on the clinostat). Using direct (invasive) sampling to obtain a sufficient number of data points at the appropriate time for monitoring the transition from lag to growth phase is somewhat challenging and tedious.  As a consequence, how gravity affects cellular density throughout the growth period is somewhat less characterized than the subsequent stationary phase of growth.

  The purpose of this project was to create an LED/photodiode system to record optical density of a growing bacterial culture during clinorotation.  The photodiode communicated with a LabVIEW  interface, which collected the data and graphed the change in voltage of the signal over time.  Growth curves were then created by correlating the voltage of the LED/photodiode system to corresponding cell counts. This apparatus enabled a pilot study to be performed that measured the lag phase duration of E. coli (ATCC 4157) grown on a clinostat for comparison to non-rotational 1g controls and similar prior space flight findings.    

(Supported by: BioServe Space Technologies NCC8-242 and a grant from the Howard Hughes Medical Institute Biological Sciences Initiative Undergraduate Research Assistantship Program, URAP)