SYMNIF · Evolution of symbiosis between ciliates and nitrogen-fixing prokaryotes
FP7 — People (Marie Curie Actions)
- Duration
- 2012-03-01 → 2014-02-28
- EU contribution
- €228,082
- Participants
- 1
- Scheme
- MC-IEF
Lines connect the coordinator with its partners.
Results in brief
Evolution of symbiosis between ciliates and nitrogen-fixing prokaryotes
Nitrogen-fixing bacteria affect the local and global nitrogen cycle by channeling gaseous nitrogen into the food web. For a long time only plant-associated diazotrophs and cyanobacteria in aquatic environments have been in scientific focus but more and more evidence show that also in the marine and freshwater systems non-cyanobacterial nitrogen-fixers can be important for actual nitrogen fixation. In this project, we studied if heterotrophic nitrogen fixers find a refuge in aquatic ciliates and if these symbionts may have an effect on the local nitrogen cycle. More than 100 ciliate strains from Danish coastal and North Atlantic open waters were studied with nifH specific PCR and acetylene reduction assay if they harbor active diazotrophic symbionts. Almost half of all tested ciliates harbored bacteria with the nifH gene. Interestingly, all ciliates from one culture showed the same results with specific PCR even with old cultures established more than 5 years ago. In addition to this observation, we found that ciliates sampled in spring and summer had a higher probability to contain diazotrophs than ciliates in winter time when the ambient water was not depleted in bioavailable nitrogen compounds. However, addition of nitrogen to the cultures showed no effect on nitrogen fixation rates highlighting the enclosed position of the symbionts. Activity measurements showed low but present nitrogen fixation and thus support the hypothesis that diazotrophic symbionts in aquatic ciliates can have high impact on local and even global matter cycling. This notion is also underlined by the fact that ciliates obtained from open water in the North Atlantic harbored diazotrophs so that nitrogen-fixing symbionts in aquatic ciliates seems to be a global phenomenon. Incubation experiments with 15N showed also nitrogen fixation in the respective size class. To study if diazotrophic symbionts can be in general important for the marine system we also investigated marine sponges and copepods. The investigated ciliates contained one to three different nitrogen fixind bacteria indicating a close and relative stable symbiosis. However, sponges with high microbial abundance (HMA) harboured only seldom diazotrophs and sponges with low microbial abundance (LMA) contained a highly diverse diazotrophic community. Copepods on the other hand harboured diverse nitrogen-fixing bacteria – even starving the copepods did not change this observation. The project highlights the importance of associated and symbiotic bacteria to global matter cycling and indicates the importance to investigate these groups of bacteria more closely than done before
Data: CORDIS, © European Union
Project objective
During the history of the planet Earth, acquisition of symbiont-encoded metabolic pathways has allowed hosts to exploit new ecological niches. A mechanistic understanding of the interactions between host and symbionts as well as knowledge about the role of symbionts in the functional diversification and species formation in hosts is, however, currently lacking. It is well known that aquatic ciliates may harbor phototrophic algae or methanogenic Archaea as symbionts. Moreover, I recently found nitrogen-fixing (diazotrophic) symbionts in ciliates (Protozoa) and recent studies report diazotrophic symbionts in marine dinoflagellates and zooplankton. Accordingly, I will in this project examine symbioses in model systems consisting of diazotrophic prokaryotes and aquatic ciliates to address the importance of symbionts for the diversification of hosts. The study implicates usage of cutting-edge microbiological, molecular and marine ecological methodologies. Various symbioses in marine and freshwater ciliates will be examined when exposed to different levels of nitrogen availability. The project will provide new insights into the formation, maintenance and specificity of symbioses between aquatic ciliates and their prokaryotic symbionts in relation to environmental conditions. These results have implications for our understanding of the importance of symbiosis in the formation of new species. Moreover, the study will provide first estimates of the nitrogen fixation of diazotrophic prokaryotes associated with ciliates. This is of relevance to the global cycling and availability of nitrogen in aquatic environments and thereby intimately linked to marine carbon budgets.""
Original text from CORDIS.
Participants
- KOBENHAVNS UNIVERSITET · KOBENHAVNCoordinatorDenmark
Links
Data: CORDIS, © European Union