[Identification, colonization and disease prevention capacity of an antagonistic bacterium against Ralstonia Solanacearum].
OBJECTIVE
To isolate a bacterial strain YPP-9, dominantly colonizing the rhizosphere of tomato using root exudate medium. In this study, we investigated the antagnism and disease-controling effect against Ralstonia solanacearum, evaluated the ability to colonize the rhizosphere of tomato, and further analyzed the phylogeny of YPP-9.


METHODS
To evaluate the antagnism against R. solanacearum and the biocontrol on tomato bacterial wilt by YPP-9 respectively employing plate culture method and pot experiment in green house. We analyzed the rhizosphere colonization of YPP-9 by PCR-denaturing gradient gel electrophoresis, and also identified the taxonomic position of YPP-9 using morphological and chemotaxonomic characteristics together with 16S rRNA gene phylogenetic analysis.


RESULTS
YPP-9 suppressed the growth of R. solanacearum (strains SSF-4) in vitro with the inhibition zone of 5 mm. The disease-control efficiency against tomato bacterial wilt in pot was 63.4%. YPP-9 also colonized the rhizosphere of tomato well. The colonies were cream in colour after 24 h culture. Cells were gram-positive, rods (1.8 -4.1 microm x 0.9 - 1.1 microm) and formed endospores. Endospores were mainly ellipsoidal to cylindrical and lied in subterminal, and occasionally paracentral, positions in no swollen sporangia. No crystal protein. The pH range for YPP-9 growth was 5.5 - 8.5 with the optimum at pH 6.0, and the temperature for YPP-9 growth was 20 to 45 degrees with the optimum at 30 degrees. The results of BIOLOG GP2 showed that YPP-9 was Bacillus. Phylogenetic analysis of the 16S rRNA gene sequence revealed that YPP-9 was the most closely related to Bacillus fumarioli, with the sequence similarity of 97.7%. The sequence number was FJ231500. The DNA G + C content was 41.9%. The major menaquinone was MK-7. The dominant fatty acids in cell wall were C14 : 0 iso, C15 : 0 iso, C16 : 0 iso and C16 : 1omega 7c alcohol, with the contents of 28.27%, 19.59%, 12.93% and 10.88%, respectively.


CONCLUSIONS
Bacterium YPP-9 strongly inhibited R. Solanacearum in vitro and efficiently suppressed the disease development in pot experiment. YPP-9 also colonized the tomato rhizosphere well. Taxonomically, YPP-9 is affiliated to Bacillus, and probably a novel species.
Li
Zhikun
Z
Guangdong Institute of Microbiology, Guangzhou Provincial Key Laboratory of Microbial Culture Collection and Application, Guangzhou Provincial Open Laboratory of Microbial New Application Technique, Guangzhou 510070, China. queenie_lee_cn@163.com
Zhu
Honghui
H
D001407:Bacillus / Q000145:classification / Q000235:genetics / Q000254:growth & development; D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000254:growth & development*; D018551:Solanum lycopersicum / Q000382:microbiology*; D010572:Pest Control, Biological / Q000379:methods*; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology* / Q000517:prevention & control*; D018517:Plant Roots / Q000382:microbiology*; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D043368:Ralstonia solanacearum / Q000254:growth & development*
D012336:RNA, Ribosomal, 16S