Screening microorganisms for insulin binding reveals binding by B urkholderia multivorans and B urkholderia cenocepacia and novel attachment of insulin to A eromonas salmonicida via the A ‐layer

Exposure to microorganisms is considered an environmental factor that can contribute to Type 1 diabetes. Insulin‐binding proteins ( IBP s) on microorganisms may induce production of antibodies that can react with the human insulin receptor ( HIR ) with possible consequences in developing a diabetic autoimmune response against HIR and insulin. The interaction of insulin with microorganisms was studied by screening 45 microbial species for their ability to bind insulin. Binding assays were performed using labelled insulin to identify insulin‐binding components on the microorganisms. B urkholderia multivorans and B urkholderia cenocepacia isolated from patients with cystic fibrosis ( CF ) and the fish pathogen A eromonas salmonicida were the only strains of those tested, which showed insulin‐binding components on their cell surfaces. Further work with A . salmonicida suggested that the insulin‐binding activity of A . salmonicida is due to the A ‐layer. A mutant of A . salmonicida lacking the A ‐layer showed binding, but at a much reduced rate suggesting another insulin‐binding component in addition to the high affinity of the A ‐protein. Soluble protein lysates were subjected to Western ligand blotting using peroxidase‐labelled insulin to detect IBP s. Two positive IBP s were apparent at approximately 30 and 20 kDa in lysates from B urkholderia strains, but no IBP was detected in A . salmonicida lysates.