Low molecular weight plant extract induces metabolic changes and the secretion of extracellular enzymes, but has a negative effect on the expression of the type-III secretion system in Xanthomonas campestris pv. campestris

Xanthomonas campestris pathovar campestris (Xcc) is a plant pathogenic bacterium and as such has to adapt to a variety of environments. During the course of disease, Xcc colonizes the surface of its host, infects the xylem in the early stages, and develops a fully saprophytic life-style, aided by secreted degradative enzymes, in the late stages. To get some insight into this complex regulation, Xcc was cultivated in the presence of low molecular weight host plant extract (<10 kDa). From this experiments it could be observed, that malate and sucrose are taken up preferably in such an environment. Furthermore, it was demonstrated, that the plant extract has a negative effect on the gene expression of the hrp-gene cluster, although the activator hrpG was induced. Also, the secretion of degradative enzymes was shown to be upregulated. These observations indicate, that a low molecular weight plant extract (<10 kDa) is a sufficient signal to regulate metabolic pathways and the secretion of enzymes relevant for the development of virulence in Xanthomonas, but has a negative effect on the expression of genes involved in type-III secretion.