title: Marine diatom species harbour distinct bacterial communities.
abstract: We examined bacterial dynamics in batch cultures of two axenic marine diatoms (Thalassiosira rotula and Skeletonema costatum). The axenic diatoms were inoculated with natural bacterial assemblages and monitored by 4,6-diamidino-2-phenolindole (DAPI) counts, denaturing gradient gel electrophoresis (DGGE) with subsequent analysis of excised, sequenced 16S rRNA gene fragments, and fluorescence in situ hybridization (FISH) with group-specific 16S rRNA oligonucleotide probes. Our results show that algal growth exhibited pronounced differences in axenic treatments and when bacteria were present. Bacterial abundance and community structure greatly depended on species, growth and physiological status of even closely related algae. Free-living and phytoplankton-associated bacteria were very different from each other and were dominated by distinct phylogenetic groups. The diatom-associated bacteria mainly belonged to the Flavobacteria-Sphingobacteria group of the Bacteroidetes phylum whereas free-living bacteria, which were rather similar in both cultures, comprised mainly of members of the Roseobacter group of alpha-Proteobacteria. Presence and disappearance of specific bacteria during algal growth indicated pronounced differences in environmental conditions over time and selection of bacteria highly adapted to the changing conditions. Tight interactions between marine bacteria and diatoms appear to be important for the decomposition of organic matter and nutrient cycling in the sea.
authors.affiliation: Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, PO Box 2503, 26111 Oldenburg, Germany. hgrossart@igb-berlin.de
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Grossart
authors.forename: Florian
authors.initials: F
authors.lastname: Levold
authors.forename: Martin
authors.initials: M
authors.lastname: Allgaier
authors.forename: Meinhard
authors.initials: M
authors.lastname: Simon
authors.forename: Thorsten
authors.initials: T
authors.lastname: Brinkhoff
mesh_terms: D020561:Alphaproteobacteria / Q000145:classification* / Q000235:genetics / Q000254:growth & development; D041963:Bacteroidetes / Q000145:classification* / Q000235:genetics / Q000254:growth & development; D004269:DNA, Bacterial / Q000032:analysis / Q000235:genetics; D017377:Diatoms / Q000254:growth & development / Q000382:microbiology*; D004586:Electrophoresis / Q000379:methods; D007211:Indoles / Q000378:metabolism; D012336:RNA, Ribosomal, 16S / Q000032:analysis / Q000235:genetics; D012623:Seawater / Q000382:microbiology*
chemical_list: D004269:DNA, Bacterial; D007211:Indoles; D012336:RNA, Ribosomal, 16S; C007293:DAPI