<i>Escherichia coli</i> adaptation to lettuce seedlings.

<p>(A) Data from individual assays of the colonization of lettuce leaves with non-adapted <i>E. coli</i> K12 strain MG1655 cultivated in LB medium (LB) or plant-adapted <i>E. coli</i> strain MG1655 freshly isolated from colonized lettuce leaves (Lett). The bars represent the median value of the data sets. (B) Competitive index (CI) analysis of the adaptation of <i>E. coli</i> K12 to colonize lettuce seedling. R_LB and G_LB are non-adapted (cultivated in LB medium) RFP- or GFP-labeled bacteria, respectively. R_LS and G_LS are RFP- or GFP-labeled, plant-adapted bacteria (isolated from colonized lettuce leaves). R_2LS are RFP-labeled bacteria adapted by two consecutive cycles of colonization of lettuce seedlings (isolated from leaves colonized with R_LS bacteria). Each data point in (A) (16 for non-adapted bacteria and 14 for adapted bacteria) corresponded to independent assays conducted at 4 to 6 different times over the course of two years. In (B) three assays per condition were conducted at two different times. Each assay (data point) consisted of three seedlings that were inoculated with bacteria in the same test tube. Differences were statistically significant (P≤0.05).</p

Chemotactic response of plant-adapted <i>Escherichia coli</i>.

<p>(A–B) Chemotactic response onto TB medium of (A) non-adapted or (B) plant-adapted bacteria. The bar in (A–B) represents 1 cm. (C–D) Chemotactic response towards (C) lettuce leaf blade or (D) lettuce-leaf main vein extracts. K12LB, non-adapted <i>E. coli</i> strain MG1655; K12, plant-adapted <i>E. coli</i> strain MG1655; RP437, non-adapted <i>E. coli</i> strain RP437 (genomic background of reference for chemotactic analysis); and RP9535, non-adapted <i>E. coli</i> strain RP9535 (Δ<i>cheA1643</i> mutation in a RP437 genomic background). Strains RP437 and RP9535 were used as control of chemotactic and non-chemotactic <i>E. coli</i> K12 bacteria. Results in C–D are statistically different (P≤0.05).</p

Effect of adaptation to lettuce leaves on <i>Escherichia coli</i> K12 tolerance to oxidative stress.

<p>Survival of (A) non-adapted bacteria (cultivated in LB medium) or (B) plant-adapted bacteria (isolated from leaves) after incubation for 0 to 8 h in the presence of (▪) 0; (Δ) 0.5; (□) 2; (◊) 8; or (○) 32 mM H₂O₂. Data represent the mean and SD of 2 independent assays.</p

Effect of disrupting the chemotactic response of <i>Escherichia coli</i> on the bacterial colonization of lettuce seedlings.

<p>(A–B) <i>E. coli</i> colonization of lettuce seedlings (A) roots or (B) leaves after inoculation with non-adapted strains RP437 or PR9535. The bars represent the median value of the datasets.</p

Representative fluorescence photomicrographs of <i>E. coli</i> K12-colonized lettuce roots.

<p>(A–D) Detail of <i>E. coli</i> localization to zones of lateral root emergence or (E–H) root elongation zone after inoculating seedlings with (A and E) RFP-, (B and F) GFP-, (C and G) non-labeled cells or (D and H) non-inoculated seedlings. Magnifications were at (A–D) 150X or (E–H) 750X. The white bar corresponds to 20 µm (A–D) or 10 µm (E–H).</p

Origin of <i>E. coli</i> cell-aggregates in roots or leaves of colonized lettuce seedlings.

<p>Representative fluorescence photomicrographs of <i>E. coli</i> K12-colonized (A) roots or (B) leaves after the inoculation of seedlings with a 1∶1 mixture of RFP- and GFP-labeled bacteria. Magnifications were at (A) 750X or (B) 150X. White bars correspond to (A) 10 µm or (B) and 20 µm.</p