The role of l-arabinose metabolism for O157:H7 in edible plants.

Arabinose is a major plant aldopentose in the form of arabinans complexed in cell wall polysaccharides or glycoproteins (AGP), but comparatively rare as a monosaccharide. l-arabinose is an important bacterial metabolite, accessed by pectolytic micro-organisms such as via pectin and hemicellulose degrading enzymes. However, not all plant-associated microbes encode cell-wall-degrading enzymes, yet can metabolize l-arabinose, raising questions about their use of and access to the glycan in plants. Therefore, we examined l-arabinose metabolism in the food-borne pathogen O157:H7 (isolate Sakai) during its colonization of plants. l-arabinose metabolism () and transport () genes were activated at 18 °C by l-arabinose and expressed over prolonged periods . Although deletion of did not impact the colonization ability of O157:H7 (Sakai) on spinach and lettuce plants (both associated with STEC outbreaks), was induced on exposure to spinach cell-wall polysaccharides. Furthermore, debranched and arabinan oligosaccharides induced metabolism gene expression , and stimulated modest proliferation, while immobilized pectin did not. Thus, O157:H7 (Sakai) can utilize pectin/AGP-derived l-arabinose as a metabolite. Furthermore, it differs fundamentally in gene organization, transport and regulation from the related pectinolytic species , reflective of distinct plant-associated lifestyles.