QUORUM SENSING IN ROOT-ASSOCIATED AND ENDOPYTIC DIAZOTROPHS

摘要

Root-associated or endophytic diazotrophs, like Azospirillum, Herbaspirillum or Burkholderia spp., are of key interest in plant-growth promotion and biological nitrogen-fixation research. Recently, new species of the genera Herbaspirillum and Burkholderia were described (Reis et al., 2004; Rothballer et al., 2006). To analyze the diazotrophic or endophytic life style of bacteria, culture dependent methods, like isolation of bacteria from surface sterilized roots in semisolid N-free media, are not sufficient. Most important for the in situ characterization of the endophytic life style are microscopic techniques. For this purpose, species-specific phylogenetic fluorescently labeled oligo-nucleotide probes (Stoffels et al., 2001) during FISH analysis and the use of GFP-tagged strains in combination with confocal laser scanning microscopy (CLSM) were used. With orthogonal views of confocal image stacks prepared with digital-image analysis tools, the endophytic colonization of plant cells can easily befollowed (Rothballer et al., 2003). TEM-based investigations after staining with monospecific polyclonal antibodies were also successfully used (Rothballer et al., unpublished data, 2007).