Carbon metabolism and catabolite repression in Rhizobium spp.

The Gram-negative soil bacteria of the family Rhizobiaceae can fonn nodules on the roots of leguminous plants and as a result are able to fix nitrogen. This partnership is highly specific as particular legumes are generally infected by one rhizobial species only (for example alfalfa by R. meliloti and soybean by B. japonicum'i. The establishment of the symbiosis is a multistepped, interactive process that requires the expression of specific plant and bacterial genes. The sequence of events necessary for symbiotic nitrogen fixation involve recognition, attachment and invasion of the legume by the bacteria, stimulation of plant cell division, multiplication and differentiation of bacteria within plant root cells into morphologically altered forms called bacteroids [1]. Nitrogen fixation by this Rhizobium-legume symbiotic association is a high-energy demanding process. The infected host plant supplies bacteroids