In their natural habitat bacteria predominantly exist as biofilms in which bacteria differ physiologically and metabolically from free-living cells. The aim of the study was to identify and characterize genes that are involved in biofilm maturation. The crystal violet (CV) assay is widely used to identify early stage biofilm mutants. However, it is not sufficiently sensitive to isolate late stage mutants that fail to develop mature biofilms. Using tetrazolium salt XTT (sodium 3'-{ l-[(phenylamino)-carbonyl]-3,4tetrazolium}- bis (4- methoxy-6-nitro) benzenesulfonic acid hydrate) this study therefore developed a more sensitive assay, named the XTT assay, to identify smaller changes in the quantity of biofilm. Using a combination of the CV and the XTT assays, a pool of transposon mediated mutant cells was screened and four genes (yhjN, adiA, bglX and glpX) were identified as potentially being involved in biofilm maturation. glpX was selected for further study. GlpX is a largely uncharacterised protein that had been shown to have FBPase activity in vitro. FBPase activity is required for the synthesis of colanic acid, a polysaccharide previously shown to playa key role in the development of the three-dimensional structure of the fully formed biofilm. The findings of this study 4 indicate that glpX-encoded FBPase activity is involved in colanic acid biosy~thesis in E. coli. A preliminary molecular analysis was made of the expression of glpX.