Diatoms are an extremely diverse group of unicellular algae characterized by an intricately ornamented siliceous cell wall consisting of two overlapping halves.¹ They form the basis of many aquatic food chains, are responsible for an estimated 20-25% of the global primary productivity,² and are major drivers of various biogeochemical cycles.^3,4,5 The total number of species is currently estimated to be as high as 200,000.⁶ Because of their key role in food chains, their high triglyceride and omega 3 fatty acid content, and their pigments and antioxidants, diatoms are useful in food and feed, aquaculture, biofuels, and biopharmaceuticals.^7,8 The nanoscale patterns of their cell walls have a high potential for application in nanotechnology and suggest structural and optical functions well beyond the current ranges used in advanced materials.⁷ They have also attracted much attention in genomic biology and biotechnology, and entire genome sequences and toolboxes for molecular biological studies are becoming available for an increasing number of species.^9,10,11 The Diatom Collection Ghent (DCG) is embedded in the Protistology & Aquatic Ecology Research Group at the Ghent University. A key aspect of the collection is that it takes into account the diatom life cycle, which typically includes a size reduction-restitution cycle.¹² Because of their rigid siliceous cell walls, strains gradually become smaller with success with successive vegetative divisions and finally die. Size increase usually only results from the expansion of a specialized cell, the auxospore, which results from sexual reproduction. This peculiarity of the diatom life cycle limits the life span of cultures of most diatoms to several months to years and is why diatoms are scarce in established culture collections.¹³ However, some species do not display the typical life cycle and avoid size reduction. As a result and despite their unusual features (in one species even the siliceous cell wall is absent), these few species have become popular model systems in physiology and in molecular and genomic biology. In DCG, the long-term maintenance of species and strains with typical life cycles is obtained through experimental manipulation of the life cycle, including the induction of auxospore formation and isolation of progeny, and cryopreservation of as many strains as possible.

The collection focuses on a limited number of strains and species, which are kept as monoclonal cultures in liquid medium and have been selected because of their potential importance for fundamental and applied research, which concentrates on model systems for the study of diatom biology and evolution and for industrial applications, such as biomass and fatty acid production for aquaculture, the food industry, and biofuels. Diatoms present in the collection include Seminavis and Cyclotella, which are being used for cell and life cycle research^13,14, and several species of Achnanthes, Eunotia, and Sellaphora, which are being used for speciation and mating system evolutionary research.^15,16,17 Species with potential for biomass and fatty acid production are currently being added. The close connection with the Protistology & Aquatic Ecology Research Group offers an opportunity for detailed characterization of the cultures, including the development of culture and preservation protocols, taxonomic identification, life-cycle characteristics, biochemical composition, as well as genetic resources such as transcriptome libraries, pedigree data and transformation protocols. This has yielded a unique set of well-characterized diatom strains.

Literature

1. Round FE, Crawford RM, Mann DG (1990) The Diatoms: Biology and Morphology of the Genera. Cambridge University Press. Cambridge. England. 747 pp.
2. Field CB, Behrenfeld MJ, Randerson JT, Falkowski P (1998) Primary production of the biosphere: integrating terrestrial and oceanic components. Science 281:237-240.
3. Bidle KD, Manganelli M, Azam F (2002) Regulation of oceanic silicon and carbon preservation by temperature control on bacteria. Science 298:1980-1984.
4. Falciatore A, Bowler C (2002) Revealing the molecular secrets of marine diatoms. Annual Review in Plant Biology 53:109-130.
5. Lopez PJ, Desclés J, Allen AE, Bowler C(2005) Prospects in diatom research. Current Opinion in Biotechnology 16:180-186.
6. Mann DG (1999) The species concept in diatoms. Phycologia 38: 437-495.
7. Bozarth A, Maier UG, Zauner S (2009) Mini-review: Diatoms in biotechnology-modern tools and applications. Applied Microbiology and Biotechnology 82:195-201.
8. Lebeau T, Robert JM. 2003. Diatom cultivation and biotechnologically relevant products. Part I: Cultivation at various scales. Applied Microbiology and Biotechnology 60:612-623.
9. Armbrust EV, Berges JA, Bowler C, Green BR, Martinez D, Putnam NH, Zhou SG, Allen AE, Apt KE, Bechner M, Brzezinski MA, Chaal BK, Chiovitti A, Davis AK, Demarest MS, Detter JC, Glavina T, Goodstein D, Hadi MZ, Hellsten U, Hildebrand M, Jenkins BD, Jurka J, Kapitonov VV, Kroger N, Lau WWY, Lane TW, Larimer FW, Lippmeier JC, Lucas S, Medina M, Montsant A, Obornik M, Parker MS, Palenik B, Pazour GJ, Richardson PM, Rynearson TA, Saito MA, Schwartz DC, Thamatrakoln K, Valentin K, Vardi A, Wilkerson FP, Rokhsar DS (2004) The genome of the diatom Thalassiosira pseudonana: Ecology, evolution, and metabolism. Science 306: 79-86.
10. Bowler C, Allen AE, Badger JH, Grimwood J, Jabbari K, Kuo A, Maheswari U, Martens C, Maumus F, Otillar RP, Rayko E, Salamov A, Vandepoele K, Beszteri B, Gruber A, Heijde M, Katinka M, Mock T, Valentin K, Verret F, Berges JA, Brownlee C, Cadoret JP, Chiovitti A, Choi CJ, Coesel S, De Martino A, Detter JC, Durkin C, Falciatore A, Fournet J, Haruta M, Huysman MJJ, Jenkins BD, Jiroutova K, Jorgensen RE, Joubert Y, Kaplan A, Kroger N, Kroth PG, La Roche J, Lindquist E,PJ, Lucas S, Mangogna M, McGinnis K, Medlin LK, Montsant A, Oudot-Le Secq MP, Napoli C, Obornik M, Parker MS, Petit JL, Porcel BM, Poulsen N, Robison M, Rychlewski L, Rynearson TA, Schmutz J, Shapiro H, Siaut M, Stanley M, Sussman MR, Taylor AR, Vardi A, von Dassow P, Vyverman W, Willis A, Wyrwicz LS, Rokhsar DS, Weissenbach J, Armbrust EV, Green BR, Van De Peer Y, Grigoriev IV (2008) The Phaeodactylum genome reveals the evolutionary history of diatom genomes. Nature 456: 239-244.
11. Poulsen N, Chesley PM, Kroger N (2006) Molecular genetic manipulation of the diatom Thalassiosira pseudonana (Bacillariophyceae). Journal of Phycology 42:1059-1065.
12. Chepurnov VA, Mann DG,Sabbe K, Vyverman W (2004) Experimental studies on sexual reproduction in diatoms. International Review of Cytology 237:156.
13. Chepurnov VA, Mann DG, von Dassow P, Vanormelingen P, Gillard J, Inze D, Sabbe K, Vyverman W (2008) My favorite cell, In search of new tractable diatoms for experimental biology. BioEssays 30:692-702.
14. Gillard J, Devos V, Huysman MJJ, Veylder LD, D'Hondt S, Martens C, Vanormelingen P, Vannerum K, Sabbe K, Chepurnov VA, Inzé D, Vuylsteke M, Vyverman W (2008) Physiological and transcriptomic evidence for a close coupling between chloroplast ontogeny and cell cycle progression in the pennate diatom Seminavis robusta. Plant Physiology 148:1394-1411.
15. Sabbe K, Chepurnov VA, Vyverman W, Mann DG (2004) Asexual auxosporulation in Achnanthes (Bacillariophyceae); development of a model system for diatom reproductive biology. European Journal of Phycology 39:327-341.
16. Vanormelingen P, Chepurnov VA, Mann DG, Sabbe K, Vyverman W (2008) Genetic divergence and reproductive barriers among morphologically heterogeneous sympatric clones of Eunotia bilunaris sensu lato (Bacillariophyta). Protist 159:73-90.
17. Behnke A, Friedl T, Chepurnov VA, Mann DG (2004) Reproductive compatibility and rDNA sequence analyses in the Sellaphora pupula species complex (Bacillariophyta). Journal of Phycology 40:193-208.

Contacts

Wim Vyverman (wim.vyverman@UGent.be)

Pieter Vanormelingen (pieter.vanormelingen@UGent.be)

Laboratory for Protistology and Aquatic Ecology
Ghent University
Krijgslaan 281, S8
B-9000 Ghent
Tel: +32 (0)9 264 85 01
Fax: +32 (0)9 264 85 99