Within the bacterial domain actinomycetes have an unusual life cycle. These microorganisms colonise dead and living organic material by means of hyphae that grow at their apices. These hyphae are part of an interconnected network, called a mycelium. After a period of vegetative growth, hyphae grow out of the substrate into the air. These aerial hyphae differentiate into chains of spores that, after dispersal, give rise to new mycelia. Actinomycetes  may also adhere to surfaces. The Claessen lab is interested in the mechanisms enabling actinomycetes to form reproductive aerial structures or to attach to surfaces. These processes depend on the formation of an extracellular matrix consisting of glycans and proteins. Notably, two classes of proteins, called chaplins and rodlins, function by assembling into so-called amyloid fibrils. Such fibrils are often associated with severe diseases in mammals (like Alzheimer’s). Our work has demonstrated that amyloids can also be beneficial to microbes enabling them to mechanically invade abiotic and biotic substrates.


  • B. Zacchetti, P. Smits & D. Claessen (2018). Dynamics of pellet fragmentation and aggregation in liquid-grown cultures of Streptomyces lividans. Front Microbiol 9: 943.
  • W. Yang, J. Willemse, E.B. Sawyer, F. Lou, W. Gong, H. Zhang, S.L. Gras, D. Claessen & S. Perrett (2017). The propensity of the bacterial rodlin protein RdlB to form amyloid fibrils determines its function in Streptomyces coelicolor. Sci Rep 7: 42876.
  • M.L.C. Petrus, E. Vijgenboom, A.K. Chaplin, J.A.R. Worrall, G.P. van Wezel & D. Claessen (2016) The DyP-type peroxidase DtpA is a Tat-substrate required for GlxA maturation and morphogenesis in Streptomyces. Open Biol 6: 150149.
  • A.K. Chaplin, M.L.C. Petrus, G. Mangiameli, M. Hough, D.A. Svistunenko, P. Nicholls, D. Claessen, E. Vijgenboom & J.A.R. Worrall (2015) GlxA is a new structural member of the radical copper oxidase family and is required for glycan deposition at hyphal tips and morphogenesis of Streptomyces lividans. Biochem J 469: 433-444.
  • W. de Jong, H.A.B. Wösten, L. Dijkhuizen & D. Claessen (2009) Attachment of Streptomyces coelicolor is mediated by amyloidal fimbriae that are anchored to the cell surface via cellulose. Mol Microbiol 73: 1128-1140.
  • M.F.B.G. Gebbink, D. Claessen, B. Bouma, L. Dijkhuizen & H.A.B. Wösten (2005) Amyloids - a functional coat for microorganisms. Nat Rev Microbiol 3: 333-341.
  • D. Claessen, R. Rink, W. de Jong, J. Siebring, P. de Vreugd, F.G.H. Boersma, L. Dijkhuizen & H.A.B. Wösten (2003) A novel class of secreted hydrophobic proteins is involved in aerial hyphae formation in Streptomyces coelicolor by forming amyloid-like fibrils. Genes Dev 17: 1714-1726.