Myo-inositol catabolism by Rhizobium in soil:: HPLC and enzymatic studies

Rhizobium loti strain NZP 2037 and R. fredii strain USDA 217 were grown in yeast-extract media containing different sugars and polyols, and the activities of several polyol dehydrogenases were measured. The specific activities of mannitol dehydrogenase and inositol dehydrogenase were greatest in mannitol-grown cells and inositol-grown cells, respectively. Inositol dehydrogenase activity was very low or absent in cells grown in all other polyols or sugars, indicating that inositol dehydrogenase is induced in response to the presence of inositol, but not other polyols or sugars. HPLC analysis of soil solutions extracted by centrifugation from three soils indicated the presence of a range of sugars, e.g. arabinose, but only one polyol, inositol. A peak corresponding to inositol was also dominant in rooting solution in which soyabean or Lotus plants had been grown. Growth of R. loti or R. fredii in sterilised soil solutions caused the disappearance of the peak corresponding to inositol (and other sugars). This was associated with the induction of inositol dehydrogenase in the cells (and other polyol dehydrogenases). These data indicate that myo-inositol is present in soil solutions and that it is metabolised by rhizobia. (C) 2001 Elsevier Science Ltd. All rights reserved.