Abstract
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.
Highlights
Plants produce a vast array of secondary metabolites, many of which are involved in defense against microbes, resulting in a dynamic coevolutionary arms race in the interaction between plants and their associated microorganisms (Burdon & Thrall, 2009)
We reasoned that if allicin-resistant bacteria were to be found in nature, it would likely be in association with garlic cloves
The degree of allicin resistance of bacteria isolated from garlic bulbs was tested in a Petri plate agar diffusion test with bacteria-seeded agar
Summary
Plants produce a vast array of secondary metabolites, many of which are involved in defense against microbes, resulting in a dynamic coevolutionary arms race in the interaction between plants and their associated microorganisms (Burdon & Thrall, 2009). Plants provide habitats for commensal and pathogenic organisms and generally it is assumed that microorganisms found in association with a given plant host are adapted to that ecological niche as part of the microbiota. Alliin lyase is one of the most prevalent soluble proteins found in garlic bulbs and leaves, and a single clove of ~10 g fresh weight can liberate up to 5 mg of allicin (Lawson et al, 1991a; Block, 2010), revealing a major investment of plant resources into this defense system (Van Damme et al, 1992; Smeets et al, 1997; Borlinghaus et al, 2014)
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