Cory Miller, Advisor: Betsy Martinez-Vaz
Sinorhizobia are bacteria capable of converting nitrogen gas to ammonia while living in close association with legumes (ex: soybeans, alfalfa and lentils). Colonization of legume roots by Sinorhizobia is essential for the optimal growth of these plants. Legumes provide 33% of the dietary protein nitrogen (N) needs of humans; therefore studying the association between Sinorhizobia and legumes is relevant to the food and agricultural industry. The goal of this study was to investigate whether similarities in the DNA profile of Sinorhizobium strains had any relationship to their geographical origin or their ability to colonize certain legume hosts. To address this question, a collection of Sinorhizobia from several geographical regions and with different levels of legume-association capabilities was examined. DNA profiles were created to assess the level of genetic diversity among the strains. Genetic profiles were obtained by DNA fingerprinting and the Repetitive Polymerase Chain Reaction Technique, REP-PCR. This procedure is based on the amplification of short repetitive DNA sequences present in bacteria. Since these organisms have different numbers of repeats in their DNA, each strain produces a unique banding pattern or fingerprint after DNA amplification. Similarities among DNA fingerprints were determined using the BioNumerics computer software and analysis of variance. The results obtained suggest that the strains analyzed can be classified in two distinct groups, S. meliloti and S. medicae, based on their fingerprinting patterns. Neither the plant host for the bacteria nor geographical origin of the strains had any relationship to the groupings.