Microorganisms play an important role in the biogeochemical cycles in terrestrial ecosystems, but also affect plant growth and health. For example, the biological reaction counterbalancing the loss of N from soils or ecosystems is the enzymatic reduction of N2 to ammonia (biological nitrogen fixation). Our main interest is a better understanding of molecular mechanisms of interactions between beneficial bacteria and plants. Our research focuses on nitrogen -fixing bacteria which are endophytes of grasses. We are particularly interested in elucidation of

1. the molecular cross-talk between the bacteria and their host,
2. the complex signal-transduction cascades allowing adaptation of bacterial reactions towards changes in the environment, and
3. the population structure, activities, roles and applications of these bacteria in the natural environment.

• Isolation, identification and taxonomic characterization of bacteria
• Assessment of their plant-beneficial traits
• Culture-independent analysis of bacterial populations and their activities in the environment by molecular methods
• Molecular tools for analysis of plant-microbe interactions (e.g. cloning and mutagenesis, transcriptomics, proteomics)
• Genome and environmental genome (metagenomic) analysis

The Kavango region of Namibia is characterized by an increasingly dense population which uses the woodlands for grazing and agricultural purposes. Cultivation and crop production ultimately decrease the fertility of those soils. Microorganisms are a vital and dominant component of the ecosystem as they significantly influence the cycling of nutrients and carbon. In the framework of a BMBF-funded BIOLOG/BIOTA South project, the aim was to assess and foster the use of nitrogen-fixing, plant-associated bacteria for a more sustainable land use and management practice. Culture-independent and culture-dependent approaches which have been developed by us were applied to study the functional diversity of diazotrophs and endophytes, and their application for a more sustainable land use. In addition the project aids in establishment of a Namibian Type Culture Collection of indigenous bacteria for future use in agriculture, medicine and biotechnology.

Small farms producing local food crops (e.g. in Kavango of Namibia, Angola) typically have only limited resources for intensive agriculture. Lack of nutrient replacement to the fields decreases soil fertility and often leads to abandoning of degraded fields and subsequent increased clearing of pristine areas. A prerequisite for a more sustainable land use and food security will be science-based improvement of productivity in local crop production by application of sustainable management practices, for which cross-border strategies can be developed. Especially the availability of nitrogen often limits plant growth and plant productivity in agriculture. Improvement of nitrogen fixation in local legumes might help to improve yields of these crops and improve soils. Problems caused by varying soil water availability in rainfed agriculture can be anticipated to increase with global warming. Research on plant-growth-promoting and biocontrol rhizobacteria (PGPR) may aid to stabilize or improve yields of typical local cereals. Examples are:

• research on bacterial inoculant that is adapted to the respective soils and the local host plants,
• analysis of symbiotic bacteria of naturally occurring root nodule symbiosis,
• identification of novel nitrogen-fixing associations with grasses
• isolation and characterization of the appropriate bacterial strains
• integration of this research into the local breeding efforts of these crops and into field trials,
• fostering application of modern breeding techniques for adapted crops.

• fostering capacity building by teaching of students, training of staff and subsequently of farmers in local training centers,
• possible training of students in our international master program (BMB, Master in Biochemistry and Molecular Biology, www.mscbmb.uni-bremen.de/en/mscbmb),
• building up a culture collection for these strains, that will preserve the biodiversity of the collected microorganisms, and ensure their supply to farmers,
• to install the appropriate microbiological facilities,
• training in modern molecular techniques such as cloning and genomic research

• training as mentioned above.

Burbano, C.S., Reinhold-Hurek, B., and Hurek, T. (2010) LNA-substituted degenerate primers improve detection of nitrogenase gene transcription in environmental samples. Environ. Microbiol. Rep. 2: 251-257.

Demba Diallo, M., Reinhold-Hurek, B., and Hurek, T. (2008) Evaluation of PCR primers for universal nifH gene targeting and for assessment of transcribed nifH pools in roots of Oryza longistaminata with and without low nitrogen input. FEMS Microbiol. Ecol. 65: 220-228.

Hurek, T., Handley, L., Reinhold-Hurek , B., and Piché, Y. (2002) Azoarcus grass endophytes contribute fixed nitrogen to the plant in an unculturable state. Mol. Plant-Microbe Interact. 15: 233-242.

Krause, A., Ramakumar, A., Bartels, D., Battistoni, F., Bekel, T., Boch, J., Böhm, M., Friedrich, F., Hurek, T., Krause, L., Linke, B., McHardy, A., Sarkar, A., Schneiker, S., Syed, A.A., Thauer, R., Vorhölter, F., Weidner, S., Pühler, A., Reinhold-Hurek, B., Kaiser, A., and Goesmann, A. (2006) Genomic insights into the lifestyle of the mutualistic, N2-fixing grass endophyte Azoarcus sp. strain BH72. Nat. Biotechnol. 24: 1385-1391.

Reinhold-Hurek, B., and Hurek, T. (1998) Life in grasses: diazotrophic endophytes. Trends Microbiol. 6: 139-144.

Tan, Z., Hurek, T., and Reinhold-Hurek, B. (2003) Effect of N-fertilization, plant genotype and environmental conditions on nifH gene pools in roots of rice. Environ. Microbiol. 5: 1009-1015.

Zhang, L., Hurek, T., and Reinhold-Hurek, B. (2007) A nifH-based oligonucleotide microarray for functional diagnostics of nitrogen-fixing microorganisms. Microb. Ecol. 53: 456-470.