In situ evidence for microdomains in the polymer matrix of bacterial microcolonies

Confocal laser scanning microscopy and fluorescent lectin-binding analyses (FLBA) were used to study the form, arrangement, and composition of exopolymeric substances (EPS) surrounding naturally occurring microcolonies in biofilms. FLBA, using multiple lectin staining and multichannel imaging, indicated that the EPS of many microcolonies exhibit distinct multiple binding regions. A common pattern in the microcolonies is a three zone arrangement with cell-associated, intercellular, and an outer layer of EPS covering the exterior of the colony. Differential binding of lectins suggests that there are differences in the glycoconjugate composition or their arrangement in the EPS of microcolonies. The combination of FLBA with fluorescent in situ hybridization (FISH) indicates that the colonies consist of the major groups, alpha- and beta-Proteobacteria. It is suggested that the EPS arrangement observed provides a physical structuring mechanism that can segregate extracellular activities at the microscale.