The effects of exopolymers on cell morphology and culturability of Leuconostoc mesenteroides during starvation

Biofilm formation by bacterial cells can be used to modify the subsurface permeability for the purpose of microbial enhanced oil recovery, bio-barrier formation, and in situ bioremediation. Once injected into the subsurface, the bacteria undergo starvation due to a decrease in nutrient supply and diffusion limitations in biofilms. To help understand the starvation response of bacteria in biofilms, the relationship between exopolymer formation and cell culturability was examined in a batch culture. The average cell diameter was observed to decrease from 0.8 μm to 0.35 μm 3 days after starvation began. Cell chain fragmentation was also observed during starvation. Cells that underwent starvation in the presence of insoluble exopolymers showed a slower rate of decrease in cell diameter and in cell chain length than cells without insoluble exopolymers. The rate of decrease in the average cell diameter and cell chain length were determined using a first order decay model. Cells starved in the presence of exopolymers showed greater culturability than cells starved without exopolymers. After 200 days starvation, 2.5 × 10⁻³% cells were culturable, but no increase in cell number was observed. During starvation, the exopolymer concentration remained constant, an indication that the exopolymer was not consumed by the starving bacteria as an alternative carbon or energy source. Received: 8 April 1999 / Received revision: 16 July 1999 / Accepted: 6 August 1999