Regional variation in the antibacterial activity of a wild plant, wild garlic (Allium ursinum L.)

Antibacterial activity is a common and highly studied property of plant secondary metabolites. Despite the extensive literature focusing on identifying novel antibacterial metabolites, little work has been undertaken to examine variation in levels of antibacterial activity in any plant species. Here, we used large-scale sampling of leaves of the antibacterial plant, wild garlic (Allium ursinum L.), assembling a set of tissue extracts from 168 plants, with 504 leaves collected and analysed. We assayed extracts for antibacterial activity against Bacillus subtilis and used LC-MS to carry out a chemometric analysis examining variation in individual metabolites, comparing them with several ecological parameters. We found that allicin was the only metabolite which was positively related to antibacterial activity. Soil temperature was a key determinant of variability in the concentrations of many foliar metabolites, however, neither allicin concentrations nor antibacterial activity was related to any of our measured ecological parameters, other than roadside proximity. We suggest that the synthesis of allicin precursors may be largely independent of growing conditions. This may be to ensure that allicin is synthesised rapidly and in sufficiently high concentrations to effectively prevent herbivory and pest damage. This finding contrasts with flavonoids which were found to vary greatly between plants and across sites. Our findings suggest that key biologically active metabolites are constrained in their concentration range compared to other compounds in the metabolome. This has important implications for the development of wild garlic as a health supplement or animal feed additive. •Variability in antibacterial activity between plants is rarely quantified.•We assembled a sample set of tissue extracts across populations of wild garlic.•Allicin was the only metabolite positively related to antibacterial activity.•Allicin concentrations were largely unrelated to ecological co-variates.•Allicin precursors may be synthesised as a competitive advantage, despite the costs.