Biofilm-Induced Gene Expression in Chemostat Grown Escherichia coli as Determined by a Gene Array

Abstract

Bio-films are attached communities of cells encased in a polysaccharide matrix that act together to increase their survival in the environment. Biofilms are the major mode of bacterial growth in nature with approximately 99% of all microbial activity occurring in them. In society, biofilms cause a variety of problems. The Centers for Disease Control estimate that 65% of all nosocomial bacterial infections are the result of biofilm activity. Bio-films can colonize surgical prostethis and result in infections that are difficult to treat with antibiotics. In industry, biofilms colonize bridges, pipes, filters and ship hulls resulting in increased corrosion and loss of profit. Previous studies have shown genes important in the initial events ofbiofilm formation, but few studies have focused on gene expression in mature biofilm growths. Gene expression patterns were studied in biofilm and plank.tonic cultures of Escherichia coli MG 1655 after a four-day growth period in a serine-limited chemostat. After four days of growth, both plank.tonic and biofilm cultures were aseptically removed and mRNA was extracted using phenol/ chloroform extraction. Radiolabeled cDNA probes were then made from the mRNA by using primers of all 4290 open reading frames in the E. coli genome. The labeled probes were hybridized to genome wide gene arrays obtained commercially. Gene expression was measured using a phosphorimager and image analysis software. Genes differentially expressed by a factor of two fold were considered significant. Out of the 4290 open reading frames in the E. coli genome, 28 genes were differentially expressed by a factor of at least two fold in either biofilm or plank.tonic cell cultures. Of the 28 genes differentially expressed, 20 genes have no known function. As a whole, the findings of this study suggest that the two growth types are similar in mature gene expression; however, any of the 20 genes of unknown function described in this study may prove vital to biofilm survival and could offer new ways of controlling them.