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 p ermeability 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 di ffusion 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 diamet er was observed to decrease from 0.8 mu m to 0.35 mu m 3 days after starvat ion began. Cell chain fragmentation was also observed during starvation. Ce lls that underwent starvation in the presence of insoluble exopolymers show ed 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 c ell diameter and cell chain length were determined using a first order deca y model. Cells starved in the presence of exopolymers showed greater cultur ability than cells starved without exopolymers. After 200 days starvation, 2.5 x 10(-3)% cells were culturable, but no increase in cell number was obs erved. During starvation, the exopolymer concentration remained constant, a n indication that the exopolymer was not consumed by the starving bacteria as an alternative carbon or energy source.