pararhizobium giardinii pararhizobium giardinii pararhizobium giardinii is a gram negative root nodule bacteria. it forms nitrogen-fixing root nodules on legumes, being first isolated from those of phaseolus vulgaris. pararhizobium giardinii scientific classification domain: bacteria phylum: pseudomonadota class: alphaproteobacteria order: hyphomicrobiales family: rhizobiaceae genus: pararhizobium species: p. giardinii binomial name pararhizobium giardinii(amarger et al. 1997) mousavi et al. 2015 biovars symbiovar giardinii symbiovar phaseoli synonyms rhizobium giardinii amarger et al. 1997