Composition and Diversity of Medicago Truncatula Root Bacterial Endophyte Populations Resulting From Growth in Different Oklahoma Soils

Abstract

The endophytic bacterial populations of surface disinfected M. truncatula root tissues collected from plants grown in a commercial growing medium and six diverse soils from across the state of Oklahoma were evaluated for diversity and differences in composition resulting from plant growth in dissimilar soils by cloning and sequencing of near full-length 16S rDNA and temperature gradient gel electrophoresis (TGGE) of 16S rDNA fragments. Cloning and sequencing of 16S rDNA revealed 36 genera of bacteria encompassing five phyla as putative M. truncatula root endophytes. Large differences in diversity were observed between endophyte populations originating from plants grown in different soils, with differences becoming increasingly pronounced at lower taxonomic levels. At the genus level, two acidic soils with a forest background and a commercial growing medium containing 15-25% ground pine bark yielded the highest endophyte diversity, while moderate diversity was observed in plants grown in managed agricultural soils. Root bacterial endophyte diversity was lowest in plants grown in soil collected from an undisturbed native tallgrass prairie. The TGGE technique failed to adequately resolve the complex endophytic bacterial 16S rDNA fragments with respect to the level of diversity revealed by the cloning approach and 16S rDNA bands on the silver-stained TGGE gel were unable to be subsequently sequenced or cloned into plasmid vectors for identification.