Biotechnological aspects of diazotrophic bacteria associated with rice

As a key prerequisite for an improvement in biological nitrogen fixation in rice, proper bacterial and plant partners have to be identified. However, there is still a lack of basic knowledge about diazotrophic bacteria which, in rice plants, are able to contribute substantially to the nitrogen nutrition of the plant. Different endophytic and rhizoplane-colonizing N-2-fixing bacteria, like Azoarcus, Azospirillum, Herbaspirillum and Burkholderia, have been described recently to occur at different densities in roots and shoots of rice plants. In contrast to certain sugar cane cultivars, where Acetobacter diazotrophicus is also thought to play a role in nitrogen fixation, a comparable highly efficient N-2-fixing system of rice cultivars and their diazotrophic bacterial partners has not yet been described. Molecular genetic tools are on hand to better characterize the diversity of the bacterial population and to investigate the localization and interaction of the bacteria in plant tissues with fluorescence-labelled oligonucleotide probes and antibodies. In addition, there are possibilities for checking and improving important ecophysiological traits of possible inoculant bacteria, which could foster their environmental fitness, inoculant potential and specific interaction with the plant host.