Interaction between plants and bacteria: glucosinolates and phyllospheric colonization of cruciferous vegetables by Enterobacter radicincitans DSM 16656.

For determining interactive plant-bacterial effects between glucosinolates and phyllospheric colonization by a plant growth-promoting strain, Enterobacter radicincitans DSM 16656, in cruciferous vegetables, the extent of bacterial colonization was assessed in 5 cruciferous vegetables (Brassica juncea, Brassica campestris, Brassica oleracea var. capitata, Brassica rapa var. alboglabra, Nasturtium officinale) using a species-specific TaqMan probe and quantitative real-time PCR. Colonization ability of inoculated E. radicincitans in the phyllosphere of these species varied from inability to colonize B. rapa up to a very good colonization rate of B. campestris. In addition to morphological factors and other plant compounds, the colonization rate was affected by different individual aromatic and aliphatic glucosinolates and their concentration, revealing that both plant pathogens and plant growth-promoting bacteria were affected by glucosinolates in their colonization behavior. In contrast, after E. radicincitans inoculation neither the total nor the individual glucosinolate concentrations in the phyllosphere of the 5 cruciferous species were affected, indicating that the nonpathogenic E. radicincitans might cause only poor cell damage by metabolizing plant cell components and does not induce a plant defense response and thus subsequently an increased glucosinolate concentration in the phyllosphere. Moreover, E. radicincitans induced no stimulation of indole glucosinolate biosynthesis by additional bacterial auxin supply.