Mikrobielle Ökologie N-Acyl-L-Homoserinlacton-produzierender Bakterien in der Rhizosphäre von Tomatenpflanzen

N-Acylhomoserinlactones (AHL) are signalling molecules in
gram-negative bacteria, which regulate, in a cell density dependent
way, important interactive functions. This phenomenon is known as
quorum-sensing. This work characterised the microbial ecology of
the autoinducer (AHL) producing bacteria Serratia liquefaciens MG1
and Pseudomonas putida IsoF in the rhizosphere of tomato plants.
Gfp- and rfp-tagged strains of the AHL producing wiltypes S.
liquefaciens MG1 and P. putida IsoF were compared with its
AHL-negative mutants, which were unable to produce AHL. Two kinds
of plants cultivating systems were used: a defined axenic system
and a complex soil system. The characterisation of the root
colonisation behaviour was performed using confocal laserscanning
microscopy (CLSM) and cell counting of bacteria. Fluorescence in
situ hybridisation (FISH) and terminal restrictions fragment length
polymorphism (t-RFLP)-techniques were used to examinate shifts of
the bacterial population in the rhizosphere on tomato plants. The
effective in situ production and spreading of AHL on tomato roots
was demonstrated with P. putida IsoF using an AHL-sensor strain P.
putida F117 pKR-C12. AHL was produced in effective concentrations
in the rhizosphere of tomato plants and influenced the bacterial
rhizosphere population. However, the AHL-production had no
influence on the colonization behaviour of the AHL-producing
strains S. liquefaciens MG1 and P. putida IsoF.