CLSM of BF01mut colonizing plant tissues. (A) Surface of maize roots and, (B) junction area, adjacent to an emerging root hair. The bacteria grew around the root hair base. Images 3A and B were taken eight days after inoculation. (C) Arabidopsis primary root tip, (D) Arabidopsis root hair. Images 3C and D were taken seven days after inoculation. (E) Lemna root covered by FB01mut biofilm. (F) Lemna frond, ventral side, colonized by FB01mut. Images 3E and F were taken nine days after inoculation.
Moreover, during prolonged incubation time (around nine days)
dense biofilms consisting of shorter, compact cells were formed.
During this process cell shape altered from rod- to dumpy barrel or
square-like structure
After eight days of growing in MS soft agar at room temperature,
the primary root of Z. mays was grown rapidly up to a length
of 20 cm. A segment of the primary root, located around 2–8cm
distant from the root tip, a region especially rich on emerging lateral
roots, was found heavily colonized by FB01mut, which formed
micro-colonies onto surface of outer epidermis cells of the primary
root (Fig. 4A) and at the junctions of primary root and lateral roots
(Fig. 4B). In general, GFP labeled bacteria were detected in decreasing
density towards root tip. A phenomenon previously reported
for tomato root colonization by P. fluorescens (Chin-A-Woeng et al.,
1997). Transmission electron microscopy (TEM) from cross sections
of maize primary root, revealed that bacterial cells colonized surface
of the root as biofilm (Davey and O’Toole, 2000) by forming
several cell layers on it (Fig. 4A). Thickness of the layer did not
exceed 2–3m as revealed by computer aided 3D-analysis of the
TEM images.