Project description:Leafy green vegetables, such as lettuce, have been increasingly implicated in outbreaks of foodborne illnesses due to contamination by Escherichia coli O157:H7. While E. coli can survive in soils, colonize plants, and survive on produce, very little is known about the interaction of E. coli with the roots of growing lettuce plants. In these studies, a combination of microarray analyses and surface enhanced Raman spectroscopy (SERS) were used to gain a comprehensive understanding of bacterial genes involved in the colonization and growth of E. coli O157:H7 on lettuce roots and compared to E. coli K12 using a hydroponic system (HS) which we have reported in the previous studies. Using microarray, after three days of interaction with lettuce roots, 94 and 109 genes of E. coli O157:H7 were significantly up-regulated and down-regulated at least 1.5 fold, respectively. Only 8 genes were also found in the E. coli K12 up-regulated genes. No genes were found in the down-regulated genes clusters between those two strains. For E. coli O157:H7, forty out of the 94 up-regulated genes (43%) were involved in protein synthesis and were highly repressed compared to 40 out of 193 (23%) E. coli K12 up-regulated genes associated with protein synthesis. The wildtype of E.coli O157:H7 colonized two log CFU per root less compared to E. coli K12. Genes involved in biofilm modulation (bhsA and ybiM) were significantly up-regulated in E. coli O157:H7 and curli production (crl and csgA) were found important for E. coli K12 to attach to lettuce roots in the previous studies. BhsA mutant of E. coli O157:H7 was impaired in the colonization of lettuce roots. The SERS spectra of E. coli K12 and O157 controls (cells without interacting with roots) were very similar. The spectra of E. coli K12 and O157 exposed to the hydroponic system (HS) showed some differences in the nucleic acid, protein, and lipid regions compared with controls. The spectra of E. coli K12 HS cells exhibited significant differences compared to spectra from E. coli O157 HS cells in the RNA and protein regions. The overall band intensity of amide regions declined for E. coli O157 HS cells, while it increased for E. coli K12 HS cells. The intensity of the RNA bands of E. coli K12 HS cells were also found much higher than those of E. coli O157 HS cells. These findings were in agreement to our Microarray data. Our microarray and SERS data showed that E. coli K12 and O157:H7 behavior dramatically differently in colonizing on lettuce roots. Compared to K12, E. coli O157:H7 colonized less efficiently on lettuce roots.

Project description:Leafy green vegetables, such as lettuce, have been increasingly implicated in outbreaks of foodborne illnesses due to contamination by Escherichia coli O157:H7. While E. coli can survive in soils, colonize plants, and survive on produce, very little is known about the interaction of E. coli with the roots of growing lettuce plants. In these studies a combination of microarray analyses and microbial genetics were used to gain a comprehensive understanding of bacterial genes involved in the colonization and growth of E. coli K12 on lettuce roots using a hydroponic assay system. Here we report that after three days of interaction with lettuce roots, 193 and 131 genes were significantly up-regulated and down-regulated at least 1.5 fold, respectively. Forty-five out of the 193 up-regulated genes (23%) were involved in protein synthesis and were highly induced. Genes involved in stress response, attachment and biofilm formation were up-regulated in E. coli when they interacted with lettuce roots under conditions of hydroponic growth. In particular crl, a gene regulating the cryptic csgA gene for curli production, was significantly up regulated. The crl, csgA and fliN mutants had a reduced capacity to attach to roots as determined by bacterial counts and by confocal laser scanning microscopy. Our microarray data showed that E. coli K12 increased the synthesis of proteins indicated that a dramatic change was induced in the physiology of the microorganism. This study indicates that E. coli K12 can efficiently colonize lettuce roots by using attachment and biofilm modulation genes and can readily adapt to the rhizosphere of lettuce plants. Further studies are needed to better characterize this interaction in pathogenic strains of this species. Escherichia coli MG1655 strains were grown in the lettuce rhizosphere for three days. Transcriptional profiling of E. coli was compared between cells grown with and without rhizosphere . Three biological replicates of each treatment were prepared, and six microarray slides were used.

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Escherichia coli

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