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CHEMICAL AND GRAVITY DEPENDENT FACTORS AFFECTING ESCHERICHIA COLI LAG PHASE TERMINATION.  R.D. Elms¹, T.A. Good¹, D.M. Klaus², M.V. Pishko³.  ¹Dept of Chemical Eng, Texas A&M Univ, ²Dept of Aerospace Science, Univ of CO, Boulder, ³Dept of Chemical Eng, Penn State Univ.

   The objectives of this study were to identify and quantify chemical compounds suspected to induce and affect bacterial lag phase termination (LPT) and to characterize the role of gravity in LPT by correlating effects on chemical concentration gradients.  The organism used for this study was E. coli ATCC 4157.     Acetic acid was not found in the extracellular environment of E. coli at the end of lag phase.  Lactic acid (LA) was found in the extracellular environment of E. coli at the end of lag phase in small amounts.  Evidence was not found to support the hypothesis that either LA or CO₂ are critical by-products for LPT.  At α = 0.05, LA (20 & 30 mg/L) supplementation increased E. coli lag phase length.  At α = 0.10, CO₂ supplementation via bubbling through 5% CO₂ in air and equilibration of media with CO₂ in a flask increased lag phase length by 1.39 and 2.12 hours, respectively.  Based on the mathematical analysis, gravity does not affect the mass transfer of LA and CO₂ away from a single E. coli cell, but does affect the mass transfer of proteins having diffusivities on the order of 1 to10 μm²/s.  Mass transfer for such proteins is greater when gravity is present.

   Evidence was not found to support the hypotheses that LA and CO₂ are critical components for LPT.  This conclusion was supported by the outcome of the supplementation experiments, and the relative movement and by-product concentration gradient analyses.  The latter two analyses indicate by-products the size of LA (D = 2200 μm²/s) and CO₂ (D = 2800 μm²/s) readily diffuse away from a single E. coli cell while by-products with D values closer to 1 to 10 μm²/s will remain at higher concentrations closer to the cell.  Therefore, working with the supposition that critical by-products are necessary for LPT it is suggested that by-products having diffusivities on the order of 1 to 10 μm²/s are likely candidates to be critical by-products for LPT.