Detailed project information

Pelagic Archaea are ubiquitously present in the oceanic water column although they are generally less diverse than Bacteria. Archaea form together with Bacteria the prokaryotic plankton of the ocean, representing the main drivers of biogeochemical cycles and playing a central role in the microbial loop of aquatic food webs. Although no representative of the pelagic, non-thermophilic Archaea has been brought into culture until very recently, advances in culture-independent methods allowed us to show that planktonic Archaea are taking up bicarbonate, thus, at least a substantial fraction of the Archaea are chemoautotrophic. This conclusion was confirmed by the first representative of a Crenarchaeum brought into culture. Apparently, some of these Crenarchaea are ammonia oxidizers as indicated by the presence of the amoA gene, a gene encoding for one of the key enzymes of ammonia oxidizers. At specific ecological conditions, these ammonia-oxidizing Crenarchaea are the dominant ammonia oxidizers in coastal systems. However, we also have evidence that not all the archaeal phylotypes are ammonia oxidizers, as indicated by the lack of the amoA gene in samples where ammonia concentrations are low.

We hypothesize that the climate change affecting the Arctic coastal waters favors Archaea relatively more than Bacteria, leading possibly to shifts in the prokaryotic community from Bacteria to Archaea dominating the prokaryotic community. This hypothesis, although untested thus far, is based on recent findings as increased melt water input increases the amount of allochthonous suspended matter in coastal Arctic systems. Crenarchaeal abundance has been found to be positively related to particle concentration. The crenarchaeal fraction of the prokaryotic community is relatively more abundant on particles than in the free-living community in coastal Arctic systems. These particles might form hot spots of ammonia oxidation as some creanarchaeal phylotypes are ammonia oxidizers while other crenarchaeal phylotypes are preferentially utilizing D-amino acids which are common in tundra soil. All these recent advances in our understanding of the ecology of marine non-thermophilic planktonic Archaea are pointing towards the fact that the recent climate changes in Arctic systems might favor Archaea over Bacteria. As planktonic Archaea are generally less diverse than Bacteria and prokaryotes are at the base of marine food webs, this hypothesized shift in the prokaryotic community might have severe consequences for coastal Arctic food webs.

Articles

• (2008). Regulation of aquatic microbial processes: the microbial loop of the sunlit surface waters and the dark ocean dissected. Aquat Microb Ecol. pp. 59-68