Diversity of Nitrogen-Fixing Bacteria Associated with Switchgrass in the Native Tallgrass Prairie of Northern Oklahoma

Abstract

ABSTRACTSwitchgrass (Panicum virgatumL.) is a perennial C4grass native to North America that is being developed as a feedstock for cellulosic ethanol production. Industrial nitrogen fertilizers enhance switchgrass biomass production but add to production and environmental costs. A potential sustainable alternative source of nitrogen is biological nitrogen fixation. As a step in this direction, we studied the diversity of nitrogen-fixing bacteria (NFB) associated with native switchgrass plants from the tallgrass prairie of northern Oklahoma (United States), using a culture-independent approach. DNA sequences from the nitrogenase structural gene,nifH, revealed over 20 putative diazotrophs from the alpha-, beta-, delta-, and gammaproteobacteria and the firmicutes associated with roots and shoots of switchgrass. Alphaproteobacteria, especially rhizobia, predominated. Sequences derived fromnifHRNA indicated expression of this gene in several bacteria of the alpha-, beta-, delta-, and gammaproteobacterial groups associated with roots. Prominent among these wereRhizobiumandMethylobacteriumspecies of the alphaproteobacteria,BurkholderiaandAzoarcusspecies of the betaproteobacteria, andDesulfuromonasandGeobacterspecies of the deltaproteobacteria.