Acetobacter diazotrophicus strains were isolated from Eleusine coracana, a new host plant cultivated along the coast of Tamil Nadu in India. Using a species-specific oligonucleotide primer and PCR amplification, the presence of this bacterium was demonstrated directly in plant tissues, proving its endophytic nature, and it was absent in non-rhizosphere soils. The isolates were also characterized on the basis of typical morphology, electron microscopy and biochemical tests, including nitrogen-fixing efficiency, to assess their diversity. When RAPD analysis was performed on the isolates, they fell into two distinct genetically related groups when compared with the type strain PA1 5 (ATCC 49037). In view of the importance of E. coracana to this region, associated nitrogen-fixing Acetobacter strains may be agronomically important because they could supply part of the nitrogen that the crop requires.