HOW DO SIMILAR SPECIES COLONIZE THE SAME ROOT?

The rhizosphere is the area of soil surrounding and influenced by the plant roots. Root bacteria need to reach the root in high numbers and to win the competition with their neighbors for niches and nutrients provided by the root.

In this study, we aim to understand how similar bacteria share the same niche by discovering genetic traits that lead to the colonization of Pseudomonas on wheat roots. Based on genomic data we isolated and characterized rhizosphere competence traits of several dominant Pseudomonas species from wheat rhizosphere. The isolates clustered into three major groups based on rpoB gene sequence: Two groups of isolates related to P. stutzeri (124.a, 128.b) and one group of P. florescence isolates (133.c). Root colonization was followed by confocal laser scanning microscopy of roots sampled from wheat plants inoculated with strains expressing fluorescent genes.

Strains 124.a and 133.c were the best root colonizers when inoculated separately, however colonizing different zones of the root (root tip vs. the upper parts). Co-inoculation of wheat roots with isolates 124.a and 133.c showed that each isolate, indeed, occupied specific niche on the root. Co-inoculation of 124.a, 128.b and 133.c showed that 133.c was dominant in the present of 124.a or 128.b and isolate 124.a, which is specialized in efficient colonization of root tips, could barely colonized the root.

Based on genome comparison between the isolates and in correlation with the described root competence traits, specific genes were selected and are currently being manipulated. Each of the manipulated strain will be examined for its colonization ability. This will allow better understanding of the genetic networks that enable Pseudomonas species to colonize wheat root and rhizosphere.