Bacterial community composition in an Arctic phytoplankton mesocosm bloom: the impact of silicate and glucose
In order to study interactions between microorganisms at different nutrient conditions in an arctic environment, a mesocosm experiment was performed in Kongsfjorden, Svalbard (79°N). A phytoplankton bloom was initiated by daily additions of mineral nutrients (ammonium and phosphate) to all mesocosm units. The addition of silicate and glucose, forming a factorial design (+Si/+C, +Si/−C, −Si/+C, −Si/−C), was intended to produce different types of growth rate limitation for the bacterial community. We here focus on the response in bacterial community composition to different nutrient situations. Phytoplankton, bacteria and viruses were enumerated by flow cytometry, while denaturing gradient gel electrophoresis (DGGE) was used to track changes in the bacterial community composition. Our results showed that both glucose and silicate addition affected the bacterial community composition, with the largest effect from glucose. The initial increase in bacterial abundance was most pronounced in the glucose units. After silicate addition, highest bacterial abundance was observed in the silicate treatments where mineral nutrient competition by diatoms was expected to be highest. The major effect of glucose was expressed by the significant separation of the +C and the −C samples at the end of the experiment, while silicate addition resulted in a more stable bacterial community structure. In the unit, given both silicate and glucose, the diatoms were totally outcompeted by the bacterial community. The competitive success of the heterotrophic bacteria in C-replete situations allows the conclusion that the bacteria were not more negatively affected by low temperatures than phytoplankton.
KeywordsBacterial community structure Nutrient competition DGGE Phytoplankton Mesocosm experiment Arctic Sea
This work was financed by the Research Council of Norway through the International Polar Year project 175939/S30 ‘PAME-Nor’ (IPY activity ID no. 71), with additional support from the strategic institution project 158936/I10 ‘Patterns in microbial diversity’, Bjerknes Centre of Climate Research, Centre of Excellence Project 146003/V30, project 178441/S40 ‘Interact’ and project 184860/S30 ‘MERCLIM’. Support was also received from Norsk Hydro Produksjon AS project number 5404889 and from the Svalbard Science Forum as ‘Aktisstipend’. We thank Kings Bay A/S and the staff at Ny Ålesund for help with logistics. Many thanks also to J. L. Ray for her helpful comments to the manuscript and Joachim Paul Spindelböck for statistical assistance.
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