Metabolomic response of Brassica rapa submitted to pre-harvest bacterial contamination

Plants are continually challenged by natural pathogens. Among a number of environmental factors, pre-harvest contamination of plants with pathogens responsible for enteric diseases in humans is of major international concern. Despite the knowledge of how bacterial attack can affect the biological system of plants, little is known about the effect of the interaction of these bacteria on plant’s metabolome. In order to investigate the metabolic change of Brassica induced by its response to different typically food borne bacteria such as Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Salmonella typhimurium and Shigella flexneri, 1H NMR and two-dimensional NMR spectra, coupled with principal component analysis (PCA) and partial least square-discriminant analysis (PLS-DA) were applied to Brassica rapa which had been subjected to these pathogens during plant growth. The metabolic changes were found to vary according to bacterial species; for example, Gram-positive and Gram-negative bacteria had a different effect on the Brassica metabolome. While threonine and GABA were found to be the discriminating metabolites in Gram-positive bacteria treated plants, those treated with Gram-negative bacteria exhibited a significant increase in sinapoyl-malate, caffeoyl-malate and histidine. The detailed study of the effect of type of bacteria showed that amino acids, alcohols, carbohydrates and phenols were discriminating metabolites. These results prove the potential of NMR-based metabolomics as a tool to study the interaction of these food-borne bacteria with vegetables.