FIG 8.

The ExpA RsmA double mutant is more virulent than either of the single mutants during infection on axenically grown tobacco seedlings. The wild-type and expA mutant strains were grown overnight in LB medium, while the double mutant (DM) and rsmA mutant were grown in the same medium for 2 days. These strains were subsequently washed twice in 10 mM MgSO₄. The washed cultures were equalized at an OD₆₀₀ of 0.1, and 1.5 μl was pipetted onto wounds in the leaves of 16-day-old in vitro tobacco seedlings. The plants were grown in sterile 24-well plates, each well containing one plant. For each experimental replicate, one 24-well plate was used for the inoculation of each strain. Inoculated plants were incubated in darkness at room temperature for 0, 24, and 48 h before the bacterial CFU from harvested plants were counted. At least six plants per plate were used to count CFU at each time point and for each strain. In the graph, CFU/plant signifies the number of CFU from the dilution series on LB plates at 0, 24, or 48 h postinfection. All comparisons of numbers of CFU/plant between the strains had a statistical significance of <0.05 using the two-tailed Welch's t test in Microsoft Excel.