title: Capsules of the diatom Achnanthidium minutissimum arise from fibrillar precursors and foster attachment of bacteria.
abstract: 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.
authors.affiliation: Konstanz Research School Chemical Biology , Germany ; Zukunftskolleg at the University of Konstanz , Germany ; Biology Department, University of Konstanz , Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Leinweber
authors.affiliation: Biology Department, University of Konstanz , Germany.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Kroth
keywords: Biofilms; Diatom-bacteria interactions; Diatoms; Energy-dispersive x-ray spectroscopy; Scanning electron microscopy
references.citation: Plant Physiol. 1997 Apr;113(4):1071-1080
references.pmid: 12223661
references.citation: Appl Environ Microbiol. 2002 Oct;68(10):4943-50
references.pmid: 12324342
references.citation: J Bacteriol. 2003 Mar;185(5):1485-91
references.pmid: 12591863
references.citation: J Gen Microbiol. 1955 Aug;13(1):162-9
references.pmid: 13252225
references.citation: PLoS Biol. 2004 Oct;2(10):e306
references.pmid: 15486572
references.citation: Proc Natl Acad Sci U S A. 1970 Sep;67(1):338-44
references.pmid: 16591861
references.citation: Biofouling. 2008;24(5):365-79
references.pmid: 18604655
references.citation: Appl Environ Microbiol. 2008 Dec;74(24):7740-9
references.pmid: 18931294
references.citation: PLoS One. 2010 Nov 02;5(11):e13794
references.pmid: 21072186
references.citation: Environ Microbiol. 2011 Apr;13(4):1052-63
references.pmid: 21244599
references.citation: Microbiol Mol Biol Rev. 2012 Sep;76(3):667-84
references.pmid: 22933565
references.citation: PLoS One. 2012;7(9):e44851
references.pmid: 23028646
references.citation: Environ Microbiol Rep. 2012 Feb;4(1):133-40
references.pmid: 23757240
references.citation: Sci Total Environ. 2014 Mar 15;475:201-15
references.pmid: 24377680
references.citation: Chem Commun (Camb). 2014 Sep 18;50(72):10441-4
references.pmid: 25061637
references.citation: J Phycol. 2015 Apr;51(2):343-55
references.pmid: 26986529
references.citation: J Phycol. 2013 Oct;49(5):937-49
references.pmid: 27007317
references.citation: J Phycol. 2009 Aug;45(4):981-6
references.pmid: 27034229
references.citation: J Phycol. 2008 Dec;44(6):1512-8
references.pmid: 27039865
references.citation: J Ultrastruct Res. 1979 Jul;68(1):16-27
references.pmid: 458930
references.citation: Plant Physiol. 1998 Apr;116(4):1431-41
references.pmid: 9536061
references.citation: Science. 1998 Jul 10;281(5374):237-40
references.pmid: 9657713