title: Diatom-associated bacteria are required for aggregation of Thalassiosira weissflogii.
abstract: Aggregation of algae, mainly diatoms, is an important process in marine systems leading to the settling of particulate organic carbon predominantly in the form of marine snow. Exudation products of phytoplankton form transparent exopolymer particles (TEP), which acts as the glue for particle aggregation. Heterotrophic bacteria interacting with phytoplankton may influence TEP formation and phytoplankton aggregation. This bacterial impact has not been explored in detail. We hypothesized that bacteria attaching to Thalassiosira weissflogii might interact in a yet-to-be determined manner, which could impact TEP formation and aggregate abundance. The role of individual T. weissflogii-attaching and free-living new bacterial isolates for TEP production and diatom aggregation was investigated in vitro. T. weissflogii did not aggregate in axenic culture, and striking differences in aggregation dynamics and TEP abundance were observed when diatom cultures were inoculated with either diatom-attaching or free-living bacteria. The data indicated that free-living bacteria might not influence aggregation whereas bacteria attaching to diatom cells may increase aggregate formation. Interestingly, photosynthetically inactivated T. weissflogii cells did not aggregate regardless of the presence of bacteria. Comparison of aggregate formation, TEP production, aggregate sinking velocity and solid hydrated density revealed remarkable differences. Both, photosynthetically active T. weissflogii and specific diatom-attaching bacteria were required for aggregation. It was concluded that interactions between heterotrophic bacteria and diatoms increased aggregate formation and particle sinking and thus may enhance the efficiency of the biological pump.
authors.affiliation: Jacobs University Bremen, School of Engineering and Science, Bremen, Germany.
authors.forename: Astrid
authors.initials: A
authors.lastname: Gärdes
authors.forename: Morten H
authors.initials: MH
authors.lastname: Iversen
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Grossart
authors.forename: Uta
authors.initials: U
authors.lastname: Passow
authors.forename: Matthias S
authors.initials: MS
authors.lastname: Ullrich
mesh_terms: D001419:Bacteria / Q000235:genetics / Q000378:metabolism; D018407:Bacterial Physiological Phenomena; D018929:Cell Culture Techniques; D017377:Diatoms / Q000378:metabolism / Q000382:microbiology* / Q000502:physiology* / Q000648:ultrastructure; D012336:RNA, Ribosomal, 16S / Q000235:genetics
chemical_list: D012336:RNA, Ribosomal, 16S
references.citation: Environ Microbiol. 2005 Jun;7(6):860-73
references.pmid: 15892705
references.citation: Photosynth Res. 1986 Jan;9(1-2):261-72
references.pmid: 24442302
references.citation: J Exp Mar Biol Ecol. 2000 Jun 1;249(1):13-27
references.pmid: 10817825
references.citation: Protoplasma. 2005 Oct;225(3-4):225-33
references.pmid: 16228900
references.citation: Microb Ecol. 1994 Sep;28(2):167-79
references.pmid: 24186443
references.citation: Cytometry. 1989 Sep;10(5):622-8
references.pmid: 2776579
references.citation: Nat Rev Microbiol. 2007 Oct;5(10):782-91
references.pmid: 17853906
references.citation: FEMS Microbiol Ecol. 2006 Apr;56(1):102-18
references.pmid: 16542409
references.citation: FEMS Microbiol Ecol. 2005 Jul 1;53(2):255-64
references.pmid: 16329945
references.citation: Protoplasma. 2007;232(1-2):69-78
references.pmid: 18157498
references.citation: FEMS Microbiol Ecol. 2007 Jan;59(1):108-17
references.pmid: 17233748
references.citation: Science. 1998 Dec 18;282(5397):2254-6
references.pmid: 9856947
references.citation: FEMS Microbiol Ecol. 2004 Mar 1;47(3):387-96
references.pmid: 19712327
references.citation: Exp Cell Res. 1986 Nov;167(1):38-52
references.pmid: 3758209
references.citation: Environ Microbiol. 2006 Jun;8(6):1074-84
references.pmid: 16689728