Bacterial community patterns along small- and large-scale environmental gradients in Arctic deep-sea sediments

One focus of this study was to detect local coherences between deep-sea benthic bacterial community patterns and an ice-edge related input of organic material (Fram Strait, Arctic Ocean) as well as physical disturbances (Ardencaple Canyon, Greenland Sea). Such large-scale patterns along a depth-dependent gradient were compared to small scales patterns within the sediment column. A further aim was to assess the local impact of small biogenic structures (Macrofaunal crawling and feeding tracks, burrows, plough traces, faeces, Tentorium semisuberites) on benthic bacterial communities by increasing microhabitat heterogeneity through the modification of near-bottom flows and hence deposition patterns in deep-sea surface sediments. As the retrieval and incubation procedures of all deep-sea sediments sampled for this study were performed in absence of pressure-retaining gears, bacterial viability and activity has been assessed by different approaches to estimate bulk metabolic pathways

<i>Frutexites</i>-like structures formed by iron oxidizing biofilms in the continental subsurface (Äspö Hard Rock Laboratory, Sweden) - Fig 2

<p>Iron oxidizing biofilms cover rocks and artificial tubes at sites NASA 1265A (A) and NASA 1127B (B) in the Äspö Hard Rock Laboratory at ca. 160 m depth. Cross sections of these <i>Frutexites</i>-like biofilms show an alternating dendritic and laminar growth, with varying contents of brown-red or blackish mineral phases (C; D). Enlarged dendritic mineralized structures within the laminae (E) and at the rim (F) of the biofilm.</p

Biomarkers detected in the total organic extract of the <i>Frutexites</i>-like biofilm from Äspö tunnel.

<p>Biomarkers detected in the total organic extract of the <i>Frutexites</i>-like biofilm from Äspö tunnel.</p

GC-MS chromatogram of the derivatized total organic extract from the <i>Frutexites</i>-like biofilm.

<p>The peak assignments are given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177542#pone.0177542.t001" target="_blank">Table 1</a>. Peaks labeled with “x” are non-derivatized fatty acids. IS = internal standard. See text for further details.</p

Sequence-based bacterial diversity of the <i>Frutexites</i>-like biofilm.

<p>The biofilm is dominated by nitrite and ammonia oxidizing bacteria (blue colors) and iron metabolizing bacteria (red colors). Both biofilms investigated show the same diversity pattern.</p

Rare earth element and yttrium (REE-Y) concentrations of the aquifer and the <i>Frutexites</i>-like biofilm (LA-ICP-MS measurements and dissolved biofilm).

<p>The amounts are given in ng/g.</p

REE data from the <i>Frutexites</i>-like biofilm and the corresponding aquifer.

<p>Note that the REE-Y pattern in the biofilms follows completely the same trend as the REE-Y pattern of the aquifer.</p

FEM images of a <i>Frutexites</i>-like biofilm.

<p>Various microbial EPS structures (A) and prokaryotic cells (B) are visible between the mineral precipitates. The dendrites (C) are covered with numerous rod-shaped microbial cells (D).</p

TEM micrographs of microbes detected in the <i>Frutexites</i>-like biofilm.

<p>The cross section of a dendritic structure shows a dense accumulation of mineral particles (A). In areas with less dense particles various microbial cells are observed (B-F). Most of the microbes are surrounded by a matrix composed of EPS and mineral particles, of either net-like (B, C, F) or laminated (D, E) structure. The dark, ca 50 nm wide square was interpreted as a magnetite produced within a magnetotactic bacterium (C). <i>Nitrotoga</i> cells were identified according to their characteristic shape and wide irregular periplasmic space (marked with P) (E). Dividing cells surrounded by a thick EPS matrix with a net like distribution of mineral particles (F).</p