Occurrence of free-living bacteria in tubers of Dioscorea yams

Both gram positive and gram negative bacteria were isolated from yam (Diosc orea spp) tubers obtained from Jamaica and Nigeria. The total bacterial cou nt and species indicated that different types of bacteria exist to varying extents in different yam tubers. An intrinsic: antibiotic resistance profil e showed that up to 83% of the strains were resistant to ampicillin (50 mu g mL(-1)), but most were sensitive to streptomycin (15 mu g mL(-1)) and kan amycin (50 mu g mL(-1)). Fourteen of the endophytes contained plasmid deoxy ribonucleic acid (DNA), seven of which possessed a single plasmid of 22 kb while the other seven had two plasmids of 22 kb and 38 kb. Bacterial isolat es from D. rotundata cv. lkale containing single and double plasmids were i dentified by fatty acid profiling as Pantoea dispersa belonging to the Erwi nia-Pantoea complex. Endonuclease restriction showed the 22 kb plasmid from endogenous P. dispersa to possess multiple restriction sites for EcoRI, Ps tI, BamHI,.SalI, HincII, MluI, and Smal. Their apparent non-pathogenic exis tence in the yam host and their genetic elements could be further explored for possible exploitation as Vectors in the genetic engineering of yam.