Bacterial Identity Cards

These are electron microscope pictures of near-identical looking bacterial flagella – the tiny tail-like structures that propel the microorganisms through fluids. According to recent research, all flagella are not the same, however, and the small differences that exist are critical to how the human immune system determines which bacteria are friendly and which are not. The principal component of flagella is flagellin, and recognition of this protein by gut immune cells can trigger an immune response. Since both friendly and pathogenic bacteria can have flagellin, scientists wondered how the immune cells tell them apart. Screening the flagellins of a variety of gut bacteria has revealed that while some bind and activate the immune cells, others bind and do not, and some don’t bind at all. Subtle differences in the amino acid sequence of the protein, it turns out, are enough to give some bacteria a free pass and others the boot.

Written by Ruth Williams

Ruth Williams

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Ruth is a freelance science journalist based in the US. She's a regular correspondent for The Scientist, and her work has appeared in The Lancet, Nature, Scientific American Mind, BBC Focus and elsewhere. Twitter @rooph

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• Image by Michael Bell, Ley Lab, Max Planck Institute
• Research by Sarah Clasen et al, Ley Lab, Department of Microbiome Science, Max Planck Institute for Biology, Tübingen, Germany
• Image copyright held by the original authors
• Research published in Science Immunology, January 2023