Chemotactic response of Escherichia coli acclimated to an endophytic lifestyle

DUBLAN M DE LOS A; ORTIZ MÁRQUEZ JC; LETT L; CURATTI L

Mar del Plata

Congreso; X Congreso Anual de la Sociedad Argentina de Microbiología General; 2014

Sociedad Argentina de Microbiología General

We have previously shown that Escherichia coli K12 strain MG1655 acclimates to colonize lettuce plants and shows increased colonization efficiencies after successive cycles of seedlings infection. The aim of this work was to investigate aspects of the acclimated state to have insights into the physiological mechanisms that E. coli display when colonizing secondary hosts such as plants. Plant-acclimated E. coli cells presented a considerably more active chemotactic response as observed as migration onto TB plates. To confirm this result migration towards glass capillaries filled with leaf-blade or vascular tissue cell-free extracts was scored as a ratio of migration towards sterile PBS buffer (control) from the same bacterial reservoir. Migration towards lettuce extracts was on average 4 to 5 fold more prominent for plant-acclimated bacteria than non-acclimated cells cultivated in LB medium. As a control we show that, conversely to its isogenic line (RP437), a mutant strain impaired in the chemotactic response (cheA- ∆cheA1643 strain RP9535) showed no preferential migration towards leaf-extracts. Bacterial counts from roots or leaves of lettuce seedlings inoculated with 10 8 non-chemotactic cells x ml-1 for 20 days were on average 15-fold lower in comparison with those reached by a similar inoculum of the chemotactic isogenic-strain. It is noteworthy that the minimal infection counts observed from the chemotactic cells were up to 1000-fold higher than those of the nonchemotactic mutant cells. After inoculation of E. coli at 105 cells x ml-1 for 14 days, three out of three pools of three seedlings per pool showed root colonization and one showed leaf colonization when inoculated with chemotactic cells. Conversely, no root or leaf colonization was observed when seedlings were inoculated with non-chemotactic bacteria in a same number of assays. Thus enhanced chemotactic response might be one of the strategies that E. coli display during acclimation to plant colonization.