Occurrence of free-living bacteria in tubers of Dioscorea yams. (250)

Samson N. Omoregie, Helen N. Asemota, Anthony U. Osagie, Sinclair Mantell, Mohammed H. Ahmad


Both gram positive and gram negative bacteria were isolated from yam (Dioscorea spp) tubers obtained from Jamaica and Nigeria. The total bacterial count and species indicated that different types of bacteria exist to varying extents in different yam tubers. An intrinsic antibiotic resistance profile showed that up to 83% of the strains were resistant to ampicillin (50 ?g mL-1), but most were sensitive to streptomycin (15 ?g mL-1) and kanamycin (50 ?g mL-1). Fourteen of the endophytes contained plasmid deoxyribonucleic 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 isolates from D. rotundata cv. Ikale containing single and double plasmids were identified by fatty acid profiling as Pantoea dispersa belonging to the Erwinia-Pantoea complex. Endonuclease restriction showed the 22 kb plasmid from endogenous P. dispersa to possess multiple restriction sites for EcoRI, Pstl, BamHI, SalI, HincII, MluI, and SmaI. Their apparent non-pathogenic existence in the yam host and their genetic elements could be further explored for possible exploitation as vectors in the genetic engineering of yam.


Dioscorea; Endogenous bacteria; Microbes; Plasmid DNA; Tubers; Antibiotic

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