Bacterial GFP tagging and analysis of rice root colonization
The isolates CT1 and CT2 were electro transformed with ca. 1 μg
of plasmid pBK-mini-Tn7 gfp1 (Koch et al., 2001) and plated onto
NA plates containing 25 μg/ml kanamycin. After 24 h of incubation
at 28°C, transformed colonies developed on the plates, and their cells
fluoresced green under the UV microscope. Colonization of the
CT6919 rice seedlings was studied in semisolid Farhåeus solution
(0.2%, w/v agar) or in vermiculite watered with Farhåeus solution.
The seedlings were inoculated for 5 days after husk removal and
surface sterilization, by dripping 100 μl of a cell suspension containing
105 cells/ml of GFP-tagged CT1 or CT2 isolates. The inoculated seedlings
were sampled at 5, 7, and 15 days after inoculation for inspection
under the fluorescence microscope (Nikon Alphaphot-2 YS2,
Japan). Roots were carefully separated with a scalpel, washed gently
with deionized water, and deposited on slides for visualization under
white or UV light using the appropriate excitation and emission filters
for GFP.