Short introduction to current research topic:

Root colonization by Herbaspirillum frisingense and Herbaspirillum hiltneri N3 in Gramineous plants

The ability of endophytic and systemic colonization of Gramineous plants is wide spread among the Herbaspirillum genus. Recently, new plant associated Herbaspirillum species have been isolated and characterized: H. frisingense from C4-fibre plants [1], H. lusitanum from root nodules of Phaseolus vulgaris [2] and during the course of this work Herbaspirillum hiltneri isolates N3, N5 and N9 from surface sterilized wheat roots [3].
These three isolates were phylogenetically analyzed. Although there was a 99.9% 16S-rDNA sequence similarity between H. lusitanum and Herbaspirillum hiltneri it had only 25% similarity in the DNA-DNA hybridization analysis. By sequencing of 23S-rDNA the calculation of a phylogenetic tree was possible, which indicated that the three isolates of Herbaspirillum hiltneri formed a distinct species among the Herbaspirillum genus. The results of a fatty acid analysis, as well as a BIOLOG assay, testing the metabolization of different carbon sources, supported this conclusion.
To study colonization behavior and growth promoting effects of isolate N3 in the rhizosphere, roots from inoculated plants grown in a monoxenic system were examined with microscopical methods. Isolate N3 was GFP tagged in order to enable the detection in uncut root material. By this, an unequivocal demonstration of the endophytic colonization by isolate N3 mainly within the intercellular spaces was possible.
A beneficial effect was detected in wheat plants inoculated with isolate N3 and Herbaspirillum frisingense after six weeks. These results clearly demonstrated the potential of this newly described species for field applications.

[1] Kirchhof et al. (2001), Int. J. Syst. Evol. Microbiol. 51: 157-168.
[2] Valverde et al. (2003), Int. J. Syst. Evol. Microbiol. 53: 1979-1983.
[3] Rothballer et al. (2006) Int. J. Syst. Evolut. Microbiol. 56: 1341-1348.

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