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ISME J. 2015 Dec;9(12):2697-711. doi: 10.1038/ismej.2015.66. Epub 2015 Apr 28.

Metagenomic and lipid analyses reveal a diel cycle in a hypersaline microbial ecosystem.

Author information

1
Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, USA.
2
Research School of Earth Sciences, The Australian National University, Canberra, ACT, Australia.
3
Department of Biological Sciences, University of Southern California, Los Angeles, CA, USA.
4
Department of Earth and Planetary Science, University of California, Berkeley, CA, USA.
5
Lawrence Berkeley National Laboratory, Life Sciences Division, Berkeley, CA, USA.
6
School of Earth Sciences, University of Melbourne, Carlton, Melbourne, Australia.
7
Department of Integrative Biology, University of Colorado Denver, Denver, CO, USA.
8
Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, USA.
9
Division of Biological Sciences, University of California, San Diego, La Jolla, CA, USA.

Abstract

Marine microbial communities experience daily fluctuations in light and temperature that can have important ramifications for carbon and nutrient cycling. Elucidation of such short time scale community-wide dynamics is hindered by system complexity. Hypersaline aquatic environments have lower species richness than marine environments and can be well-defined spatially, hence they provide a model system for diel cycle analysis. We conducted a 3-day time series experiment in a well-defined pool in hypersaline Lake Tyrrell, Australia. Microbial communities were tracked by combining cultivation-independent lipidomic, metagenomic and microscopy methods. The ratio of total bacterial to archaeal core lipids in the planktonic community increased by up to 58% during daylight hours and decreased by up to 32% overnight. However, total organism abundances remained relatively consistent over 3 days. Metagenomic analysis of the planktonic community composition, resolved at the genome level, showed dominance by Haloquadratum species and six uncultured members of the Halobacteriaceae. The post 0.8 μm filtrate contained six different nanohaloarchaeal types, three of which have not been identified previously, and cryo-transmission electron microscopy imaging confirmed the presence of small cells. Notably, these nano-sized archaea showed a strong diel cycle, with a pronounced increase in relative abundance over the night periods. We detected no eukaryotic algae or other photosynthetic primary producers, suggesting that carbon resources may derive from patchily distributed microbial mats at the sediment-water interface or from surrounding land. Results show the operation of a strong community-level diel cycle, probably driven by interconnected temperature, light abundance, dissolved oxygen concentration and nutrient flux effects.

PMID:
25918833
PMCID:
PMC4817636
DOI:
10.1038/ismej.2015.66
[Indexed for MEDLINE]
Free PMC Article

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