Genetic and molecular characterization of multicomponent resistance of Pseudomonas against allicin

A pseudomonad isolated from garlic has multiple copies of genes on three genomic islands that confer resistance to allicin, a secondary plant product and defense substance that causes disulfide stress.
The common foodstuff garlic produces the potent antibiotic defense substance allicin after tissue damage. Allicin is a redox toxin that oxidizes glutathione and cellular proteins and makes garlic a highly hostile environment for non-adapted microbes. Genomic clones from a highly allicin-resistant Pseudomonas fluorescens (PfAR-1), which was isolated from garlic, conferred allicin resistance to Pseudomonas syringae and even to Escherichia coli. Resistance-conferring genes had redox-related functions and were on core fragments from three similar genomic islands identified by sequencing and in silico analysis. Transposon mutagenesis and overexpression analyses revealed the contribution of individual candidate genes to allicin resistance. Taken together, our data define a multicomponent resistance mechanism against allicin in PfAR-1, achieved through horizontal gene transfer.