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Aquatic Microbial Ecology

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AME 50:11-24 (2007)  -  DOI:

Stratification of the microbial community inhabiting an anchialine sinkhole

J. R. Seymour1,3,*, W. F. Humphreys2, J. G. Mitchell1

1Flinders University of South Australia, School of Biological Sciences, PO Box 2100, Adelaide, South Australia 5001, Australia
2Western Australian Museum, Locked Bag 49, Welshpool DC, Western Australia 6986, Australia
3Present address: Massachusetts Institute of Technology, Department of Civil & Environmental Engineering, 77 Massachusetts Ave., Cambridge, Massachusetts 02139, USA

ABSTRACT: Bundera Sinkhole in northwestern Australia is an anchialine ecosystem characterised by a highly stratified water column comprising a complex polymodal profile of several physico-chemical parameters. We studied the microscale and finescale dynamics of the resident microbial community within the sinkhole. Sub-millimetre scale distributions of phytoplankton abundance were measured in the top 8 m of the water column using a free-falling high resolution fluorometer. Depth profiles were characterised by a strong, 10 to 20 cm layer of elevated fluorescence, occurring at approximately 1 m depth, which despite changes in magnitude and width was found to persist during a 24 h sampling period. Near surface distributions of microbial populations were measured using a syringe sampling profiler, which allowed for collection of water samples at 5 cm resolution, and flow cytometric analysis. These samples revealed a complex microbial assemblage, with multiple sub-populations of viruses, bacteria and picophytoplankton present throughout the water column. Within 3 m profiles, the bacterial and virus populations showed marked shifts in relative abundance, with changes of over 35-fold observed across as little as 20 cm. Samples collected from the surface to a depth of 30 m by divers also revealed distinct peaks and layers in the relative abundance of the different bacteria and virus sub-populations, which often corresponded to heterogeneities in chemical and nutrient parameters, and at some depths indicated the prevalence of chemolithotrophic populations. The complex patterns described here represent the first comprehensive observations of microbial spatiotemporal dynamics throughout an anchialine ecosystem and reveal a highly structured microbial habitat consisting of discrete niches, each dominated by heterotrophic, phototrophic or chemoautotrophic microorganisms.

KEY WORDS: Anchialine · Sinkhole · Bacteria · Stratification · Chemoautotrophy · Virus ·Phytoplankton

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Cite this article as: Seymour JR, Humphreys WF, Mitchell JG (2007) Stratification of the microbial community inhabiting an anchialine sinkhole. Aquat Microb Ecol 50:11-24.

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