Transcriptomic analysis for genetic mechanisms of the factors related to biofilm formation in Escherichia coli O157:H7

Abstract

Two lineages of enterohemorrhagic Escherichia coli O157:H7 (EDL933, Stx1(+) and Stx2(+)) and 86-24 (Stx2(+)) were investigated to determine the genetic basis of biofilm formation on abiotic surfaces. Strain EDL933 formed a robust biofilm while strain 86-24 formed almost no biofilm on either polystyrene plates or polyethylene tubes. Whole-transcriptome profiles of EDL933 versus 86-24 revealed that in the strong biofilm-forming strain, genes involved in curli biosynthesis and cellulose production were significantly induced, whereas genes involved in indole signaling were most repressed. Additionally, 49 phage genes were highly induced and repressed between the two strains. Curli assays using Congo red plates and scanning electron microscopy corroborated the microarray data as the EDL933 strain produced a large amount of curli, while strain 86-24 formed much less curli. Moreover, EDL933 produced 19-fold more cellulose than 86-24, and indole production in EDL933 was two times lower than that of the strain 86-24. Therefore, it appears E. coli O157:H7 EDL933 produces more biofilm because of its increased curli and cellulose production and reduced indole production.

Fig. 1

Biofilm formation of the two E. coli O157:H7 strains, EDL933 and 86-24, in 96-well polystyrene plates (A) and in polyethylene tubes (B) in LB medium without shaking at 37°C after 24 h. At least four independent experiments were conducted (a total 12 wells), and error bars indicate one standard deviation.

Fig. 2

Curli formation of the two E. coli O157:H7 strains, EDL933 and 86-24. Curli production at 37°C after 24 h was observed using Congo red plates (A) and SEM (B). For SEM analysis, planktonic cells were grown in LB medium to turbidity of 2.0. The inset shows the magnified amorphous curli/cellulose matrix.