exemplary embodiments are directed to a herbicide resistant n 2 - fixing microorganism and to a method for enhancing n 2 fixation by the herbicide resistant rhizobia in symbiosis with herbicide resistant or tolerant leguminous plants treated with herbicide . at least one preferred embodiment comprises mutant rhizobia strains selected based on tolerance of the broad spectrum glyphosate weed control agent , originally roundup ®. preferred embodiments can be expected to outcompete both indigenous soil rhizobia and / or commercial rhizobia that are not resistant to the herbicide .