Abstract
The objectives of this study were to identify and quantify chemical compounds suspected to induce and affect bacterial lag phase termination and to characterize the role of gravity in lag phase termination by correlating effects on chemical concentration gradients. The organism used for this study was Escherichia coli ATCC 4157. Acetic acid was not found in the extracellular environment of E. coli at the end of lag phase. Lactic acid 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 lactic acid or CO₂ are critical by-products for lag phase termination. At a significance level of α = 0.05, lactic acid (20 and 30 mg/L) supplementation increased E. coli lag phase length. At a significance level of α = 0.10, CO₂ supplementation via bubbling through 5% CO₂ in air from a pressurized canister and equilibration of media with CO₂ in a flask increased lag phase length by 1.39 and 2.12 hours, respectively. Based on mathematical analysis, gravity does not affect the mass transfer of lactic acid 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 []m²/s. Mass transfer for such proteins is greater when gravity is present. Evidence was not found to support the hypotheses that lactic acid and CO₂ are critical components for lag phase termination. 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 lactic acid (D = 2200 []m²/s) and CO₂ (D = 2800 []m²/s) readily diffuse away from a single E. coli cell while by-products with diffusivities closer to 1 to 10 []m²/s will remain at higher concentrations closer to the cell. Therefore, working with the supposition that critical by-products are necessary for lag phase termination it is suggested that by-products having diffusivities on the order of 1 to 10 []m²/s are likely candidates to be critical by-products for lag phase termination.
Elms, Rene ̓Davina (2002). Chemical and gravity dependent factors affecting Escherichia coli lag phase termination. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -2002 -THESIS -E46.