- Rhizobium leguminosarum exoB mutants are deficient in the synthesis of UDP-glucose 4'-epimerase. Canter Cremers, H.C., Batley, M., Redmond, J.W., Eydems, L., Breedveld, M.W., Zevehuizen, L.P., Pees, E., Wijffelman, C.A., Lugtenberg, B.J. J. Biol. Chem. (1990)