Microbial diversity and function within the salinity gradient of the Baltic Sea
Zusammenfassung der Projektergebnisse
Salinity is a major environmental factor, which determines the composition and distribution of microorganisms in the Baltic Sea. However, neither the underlying mechanisms nor the functional consequences are well understood yet. Within this project we aimed to (i) extend the current knowledge on the diversity and abundance of planktonic and benthic microorganisms along salinity gradients in the Baltic Sea, (ii) to investigate adaptations and assembly mechanisms of bacterial communities in response to salinity changes, and (iii) to test whether salinity-driven shifts in bacterial composition imply functional changes. To achieve these goals, we used a combination of field sampling during several cruises, covering nearly the entire Baltic Sea, and incubation experiments with natural microbial communities. The field data revealed a characteristic distribution of bacterioplankton phylogenetic groups across the Baltic Sea, and it became evident that the phylogenetic signal for salinity was preserved on a higher taxonomic level compared to seasonal differences. A marine-brackish transition was even found among the SAR11 clade, in which the marine subclade is replaced by a brackish subclade in the central Baltic Sea. The chloroplasts 16S rRNA genes were used to demonstrate also a distinct distribution pattern in phytoplankton composition along the salinity gradient. Salinity proved to be also a major determinant of the upper sediment bacterial communities, which were analysed for selected stations across the different salinity zones, from the marine Skagerrak to the nearly limnic Bothnian Bay. For examining functional consequences of salinity-induced bacterial diversity shifts, different types of incubation experiments with collected water from representative stations of the different salinity zones were conducted. The utilisation of riverine, terrestrial DOM (tDOM) was examined in mesocosms with marine, meso-haline and oligo-haline bacterial communities. The results suggest that oligohaline bacterial communities are particularly adapted to degrade tDOM that enters the Northern Baltic Sea. In addition to the evaluation of field samples, we implemented a transplant experiment to investigate the impact of changing salinity on the locally adapted Baltic bacterioplankton by exposing bacteria from three distinct salinity regions of the Baltic Sea to each other’s environmental conditions. We found that marine Baltic sea bacteria were viable and achieved high abundance outsize of their native salinity zone. Further, different ecological strategies were identified in response to salinity changes, habitat specialists and generalists. Habitat specialists are particularly promoted by large salinity changes, and environmental filtering is the dominant assembly mechanisms for this group. For assessing functional redundancy (FR) of bacterial communities, a new metatranscriptomic-based approach was introduced and tested, which allows to assess multifunctional aspects of FR.
Projektbezogene Publikationen (Auswahl)
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(2014). Diversity and abundance of “Pelagibacterales” (SAR11) in the Baltic Sea salinity gradient. Systematic and Applied Microbiology 37: 601–604
Herlemann, DPR., Woelk, J., Labrenz, M., Jürgens, K.
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(2016). Phylogenetic signals of salinity and season in baceterial community composition across the salinity gradient of the Baltic Sea. Frontiers in Microbiology 7: 1883
Herlemann, DPR., Lundin, D., Andersson, A.F., Labrenz, M., Jürgens, K.
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(2017). Differential responses of marine, mesohaline and oligohaline bacterial communities to the addition of terrigenous carbon. Environmental Microbiology 19: 3098-3117
Herlemann, DPR., Manecki, M., Dittmar, T., Jürgens, K.
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(2017). Metatranscriptomic data reveal the effect of different community properties on multifunctional redundancy. Molecular Ecology 26: 6813-6826
Beier, S., Shen, D., Schott, T., Jürgens, K.
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(2018): Benthic bacterial community composition in the oligohaline-marine transition of surface sediments in the Baltic Sea based on rRNA analysis. Frontiers in Microbiology 9:236
Klier, J., Dellwig, O., Leipe, T., Jürgens, K., Herlemann, D.P.R.
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(2018): Dispersal modifies the diversity and composition of active bacterial communities in response to a salinity disturbance. Frontiers in Microbiology
Shen, D., Langenheder, S., Jürgens, K.
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(2018): Experimental insights into the importance of ecologically dissimilar bacteria to community assembly along a salinity gradient. Environmental Microbiology 20: 1170-1184
Shen, D., Jürgens, K., Beier, S.
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2018. The distribution of phytoplankton in the Baltic Sea assessed by a prokaryotic 16S rRNA gene primer system. Journal of Plankton Research 40: 244-254
Bennke, C. M., Pollehne, F., Müller, A., Hansen, R., Kreikemeyer, B., Labrenz, M.
