Delaying the growth of <italic>Leuconostoc mesenteroides</italic> NRRL-B523 in batch and porous matrix systems.

Abstract

Bacterial profile modification is an enhanced oil recovery technique that directs injected water into a reservoir's low permeability zone containing trapped crude oil. During field implementation of <italic> in-situ</italic> exopolymer production, well bore face plugging may significantly reduce the extent of depth penetration by injected bacteria. Slowing the growth rate, lengthening the lag phase, and reducing the dextran polymerization rate were investigated as methods to delay biopolymer gelation and extend the depth of the polymer plug. High substrate concentrations, an alkaline pH, and the addition of the growth inhibitors sodium dodecyl sulfate and sodium benzoate altered the batch growth kinetics of <italic>L. mesenteroides</italic> NRRL-B523. A medium containing 500 g/l sucrose produced a lag time of twelve hours. At a threshold pH value of 8.1, an average lag time of 190 hours was observed. Higher pH values prevented growth. In a medium containing 500 g/l sucrose and a suboptimal pH, exponential growth was delayed until the pH, reduced by the acid byproducts of fermentation, reached a critical value of 6.79. A mathematical model was developed to describe the relationship between growth rate, lag time, and medium pH. Sodium benzoate addition linearly reduced the growth rate to zero at 0.6% but did not alter lag time. A 0.075 mM sodium dodecyl sulfate solution inhibited growth. Flow experiments were performed in a micromodel and a porous ceramic linear core flood system. Micromodel studies enabled the visualization of biomass formation and evolution. Core flood experiments demonstrated a permeability reduction delay of 90 hours. A continuum mathematical model incorporating bacterial growth, dextran production, and fluid shear agreed with experimental results. Attempts were made to measure the membrane proton motive force and determine the cellular mechanism controlling the lag phase duration. Two methods of measuring the intracellular pH, using a membrane-permeable fluorescent dye and transforming <italic>L. mesenteroides</italic> with a green fluorescent protein gene, failed to yield quantitative results.