The modification of the flavonoid naringenin by bradyrhizobium sp. strain ORSZ85 changes the nod genes inducer function to a growth stimulator

Abstract

As inducers of nodulation (now genes, flavonoids play an important role in the symbiotic interaction between rhizobia and legumes However, in addition to the control of expression of nod genes, many other elfects of flavonoids on rhizobial cells have been described. Here, we show that the flavonoid naringenin stimulates the growth of the photosynthetic Bradyrhizobium sp. strain ORS285. This growth-stimulating effect was still observed for strain ORS285 with nole, nodDZ, or the naringenindegrading fde operon deleted. Phenotypic microarray analysis indicates that in cells grown in the presence of naringenin, the glycerol and fatty acid metabolism is activated. Moreover, electron microscopic and enzymatic analyses show that polyhydroxy alkanoate metabolism is altered in cells grown in the presence of naringenin. Although strain ORS285 was able to degrade naringenin, a fraction was converted into an intensely yellowcolored molecule with an m/z (+) of 363.0716. Further analysis indicates that this molecule is a hydroxylated and O-methylated form of naringenin. In contrast to naringenin, this derivative did not induce nod gene expression, but it did stimulate the growth of strain ORS285. We hypothesize that the growth stimulation and metabolic changes induced by naringenin are part of a mechanism to facilitate the colonization and infection of naringeninexuding host plants.