TY - JOUR UR - https://doi.org/10.7717/peerj.858 DO - 10.7717/peerj.858 TI - Capsules of the diatom Achnanthidium minutissimum arise from fibrillar precursors and foster attachment of bacteria AU - Leinweber,Katrin AU - Kroth,Peter G. A2 - Smidt,Hauke DA - 2015/03/26 PY - 2015 KW - Biofilms KW - Diatoms KW - Scanning electron microscopy KW - Energy-dispersive x-ray spectroscopy KW - Diatom-bacteria interactions AB - Achnanthidium minutissimum is a benthic freshwater diatom that forms biofilms on submerged surfaces in aquatic environments. Within these biofilms, A. minutissimum cells produce extracellular structures which facilitate substrate adhesion, such as stalks and capsules. Both consist of extracellular polymeric substance (EPS), but the microstructure and development stages of the capsules are so far unknown, despite a number of hypotheses about their function, including attachment and protection. We coupled scanning electron microscopy (SEM) to bright-field microscopy (BFM) and found that A. minutissimum capsules mostly possess an unstructured surface. However, capsule material that was mechanically stressed by being stretched between or around cells displayed fibrillar substructures. Fibrils were also found on the frustules of non-encapsulated cells, implicating that A. minutissimum capsules may develop from fibrillar precursors. Energy-dispersive X-ray (EDX) spectroscopy revealed that the capsule material do not contain silicon, distinguishing it from the frustule material. We furthermore show that bacteria preferentially attach to capsules, instead of non-encapsulated A. minutissimum cells, which supports the idea that capsules mediate diatom-bacteria interactions. VL - 3 SP - e858 T2 - PeerJ JO - PeerJ J2 - PeerJ SN - 2167-8359 ER -