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Bacteria degrading the quorum-sensing (QS) signal molecule N-hexanoylhomoserine lactone were isolated from a tobacco rhizosphere. Twenty-five isolates degrading this homoserine lactone fell into six groups according to their genomic REP-PCR and rrs PCR-RFLP profiles. Representative strains from each group were identified as members of the genera Pseudomonas, Comamonas, Variovorax and Rhodococcus. All these isolates degraded N-acylhomoserine lactones other than the hexanoic acid derivative, albeit with different specificity and kinetics. One of these isolates, Rhodococcus erythropolis strain W2, was used to quench QS-regulated functions of other microbes. In vitro, W2 strongly interfered with violacein production by Chromobacterium violaceum, and transfer of pathogenicity in Agrobacterium tumefaciens. In planta, R. erythropolis W2 markedly reduced the pathogenicity of Pectobacterium carotovorum subsp, carotovorum in potato tubers. These series of results reveal the diversity of the QS-interfering bacteria in the rhizosphere and demonstrate the validity of targeting QS signal molecules to control pathogens with natural bacterial isolates.

Research has been conducted on the soil rhizosphere bacterial communities. The role of putA gene and Sinorhizobium meliloti strain M401 in these communities has been investigated and the results are reported.

Research has been conducted on the ammonia-oxidizing bacteria. The detection and characterization of these bacteria from the rhizosphere roots carried out via PCR and denaturing gradient gel electrophoresis which target amoA gene are described.

Research has been conducted on the plasmid plPO2 isolated from the wheat rhizosphere. The nucleotide sequence and genetic organization of this plasmid have been investigated and the details are reported.

Fungal diversity in the wheat rhizosphere was analyzed using polymerase chain reaction (PCR) primers for the specific amplification of fungal 18S rDNA and temperature gradient gel electrophoresis. DNA was extracted from the wheat rhizosphere, and 18S rDNA gene banks were constructed in Escherichia coli by cloning PCR products generated with primer pairs. The primer pair EF4-EF3 appeared slightly biased to amplify Basidiomycota and Zygomycota, whereas EF4-fung5 amplified mainly Ascomycota.

The potential effects of transgenic aspen overexpressing a polyphenol oxidase gene on diversity in rhizosphere communities are assessed. The cultivation-independent methods have disclosed only minor differences between the bacterial and fungal communities associated with transgenic and unmodified trees.

The onset of streptothricin (ST) biosynthesis in Streptomyces rochei F20 is analyzed by using reverse transcription-PCR (RT-PCR) to detect transcripts of ST genes during growth in liquid medium, soil and the rhizosphere. The results suggests that neither ST resistance (sttR) nor biosynthesis (sttA) transcripts were detected by RT-PCR in the rhizoplane, which supported a lower population density of F20 than the rhizosphere.

Research has been conducted on Pseudomonas sp. strain BW11M1 isolate which produces antibacterial compound active against P. putida GR12-2R3. Results demonstrate that this compound is putidacin, and the cloning and characterization of the gene encoding this putidacin are described.