Friend or Foe? The influence of bacteria on the growth of the diatom Thallassiosira rotula.

• Main Author: Drewes, Hannah Marie
• Format: Thesis
• Language: unknown
• Published: 2022
• Subjects: Arctic; Helgoland
• Online Access: https://epic.awi.de/id/eprint/56704/; https://hdl.handle.net/10013/epic.19541f83-59cc-427e-92c8-6fa07777f283

Diatom-bacteria interactions are a crucial part of the global ocean and span from mutualistic via competitive to parasitic relationships. A lot of these interactions take place in the so-called “phycosphere” a diffusive boundary layer surrounding algal cells providing bacteria with a unique environment rich in algal-derived carbon sources. However, only few bacterial lines (Alpha-, Beta- and Gammaproteobacteria, Bacteroidetes) mainly genera such as Roseobacter, Sulfitobacter and Flavobacterium have been observed to reliably form symbiosis with diatom species. Thalassiosira rotula is a ubiquitous, bloom-forming, centric diatom found in a diverse number of marine habitats and was in this case isolated from a spring bloom event around the island of Helgoland. The main objective of this thesis was to investigate the influence of single strain bacteria on the growth of Thalassiosira rotula. To achieve this goal a co-cultivation method was designed that allowed for a high number of bacteria strains to be investigated at the same time. Moreover, it was investigated whether co-cultivation with two bacterial strains at the same time enhanced, diminished or did not affect the effect of single-strain bacteria on the growth of T. rotula. T. rotula was grown under vitamin-reduced conditions in Enriched Seawater, Artificial Water (ESAWred) in 24-well plates in co-cultivation with 33 bacterial strains isolated from the same spring bloom event or from the Arctic. Autofluorescence of algae was measured in a microplate reader as a proxy for algal growth over time. Moreover, two, dual-strain co-cultivations were conducted where T. rotula was combined with two different bacterial strains at the same time. During three single-strain co-cultivations it was observed that the designed method had two major sources of errors: 1) Algal growth was stunted by an unknown effect of MB medium introduced into cultures with bacterial inoculates 2) Bacterial OD600 varied greatly with the same dilution factor, therefore a fourth, improved ...