Microbial community composition and function in permanently cold seawater and sediments from an arctic fjord of svalbard - PubMed (original) (raw)

Microbial community composition and function in permanently cold seawater and sediments from an arctic fjord of svalbard

A Teske et al. Appl Environ Microbiol. 2011 Mar.

Abstract

Heterotrophic microbial communities in seawater and sediments metabolize much of the organic carbon produced in the ocean. Although carbon cycling and preservation depend critically on the capabilities of these microbial communities, their compositions and capabilities have seldom been examined simultaneously at the same site. To compare the abilities of seawater and sedimentary microbial communities to initiate organic matter degradation, we measured the extracellular enzymatic hydrolysis rates of 10 substrates (polysaccharides and algal extracts) in surface seawater and bottom water as well as in surface and anoxic sediments of an Arctic fjord. Patterns of enzyme activities differed between seawater and sediments, not just quantitatively, in accordance with higher cell numbers in sediments, but also in their more diversified enzyme spectrum. Sedimentary microbial communities hydrolyzed all of the fluorescently labeled polysaccharide and algal extracts, in most cases at higher rates in subsurface than surface sediments. In seawater, in contrast, only 5 of the 7 polysaccharides and 2 of the 3 algal extracts were hydrolyzed, and hydrolysis rates in surface and deepwater were virtually identical. To compare bacterial communities, 16S rRNA gene clone libraries were constructed from the same seawater and sediment samples; they diverged strongly in composition. Thus, the broader enzymatic capabilities of the sedimentary microbial communities may result from the compositional differences between seawater and sedimentary microbial communities, rather than from gene expression differences among compositionally similar communities. The greater number of phylum- and subphylum-level lineages and operational taxonomic units in sediments than in seawater samples may reflect the necessity of a wider range of enzymatic capabilities and strategies to access organic matter that has already been degraded during passage through the water column. When transformations of marine organic matter are considered, differences in community composition and their different abilities to access organic matter should be taken into account.

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Figures

FIG. 1.

FIG. 1.

Hydrolysis rates of polysaccharides and plankton extracts in surface-water (horizontal-stripe bars) and bottom-water (slanted-stripe bars) samples (A) and in homogenized sediments from depths of 0 to 2 cm (gray bars) and 3 to 9 cm (black bars) (B). Substrates are pull, pullulan; lam, laminarin; xyl, xylan; fu, fucoidan; ara, arabinogalactan; chon, chondroitin sulfate; alg, alginic acid; iso, Isochrysis extract; spir, Spirulina extract; wak, wakame extract. Error bars show standard deviations of triplicate incubations. An asterisk indicates no data.

FIG. 2.

FIG. 2.

Percent representation of bacterial phylum- and subphylum-level groups in 16S rRNA gene clone libraries from water column and sediment samples in Smeerenburg Fjord, Svalbard. From left to right, surface water, deep water, surface sediment, and deep sediment community. cmbsf, centimeters below the surface.

FIG. 3.

FIG. 3.

Neighbor-joining phylogeny of Smeerenburg Fjord alpha- and deltaproteobacterial phylotypes, based on an ∼1,200-bp alignment of bacterial 16S rRNA sequences. The Svalbard phylotypes are labeled with the habitat indicator (water_surface, water_deep, sediment_surface, sediment_deep), followed by the clone number, and are highlighted in boldface.

FIG. 4.

FIG. 4.

Neighbor-joining phylogeny of Smeerenburg Fjord Bacteroides phylotypes, based on an ∼1,200-bp alignment of bacterial 16S rRNA sequences. The Svalbard phylotypes are labeled with the habitat indicator (water_surface, water_deep, sediment_surface, sediment_deep), followed by the clone number, and are highlighted in boldface.

FIG. 5.

FIG. 5.

Neighbor-joining phylogeny of Smeerenburg Fjord beta- and gammaproteobacterial phylotypes, based on an ∼1,200-bp alignment of bacterial 16S rRNA sequences. The Svalbard phylotypes are labeled with the habitat indicator (water_surface, water_deep, sediment_surface, sediment_deep), followed by the clone number, and are highlighted in boldface.

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