Substrate-specific pressure-dependence of microbial sulfate reduction in deep-sea cold seep sediments of the Japan Trench

Abstract

The influence of hydrostatic pressure on microbial sulfate reduction (SR) was studied using sediments obtained at cold seep sites from 5500 to 6200 m water depth of the Japan Trench. Sediment samples were stored under anoxic conditions for 17 months in slurries at 4°C and at in situ pressure (50 MPa), at atmospheric pressure (0.1 MPa), or under methanic conditions with a methane partial pressure of 0.2 MPa. Samples without methane amendment stored at in situ pressure retained higher levels of sulfate reducing activity than samples stored at 0.1 MPa. Piezophilic SR showed distinct substrate specificity after hydrogen and acetate addition. SR activity in samples stored under methanic conditions was one order of magnitude higher than in non-amended samples. Methanic samples stored under low hydrostatic pressure exhibited no increased SR activity at high pressure even with the amendment of methane. These new insights into the effects of pressure on substrate specific sulfate reducing activity in anaerobic environmental samples indicate that hydrostatic pressure must be considered to be a relevant parameter in ecological studies of anaerobic deep-sea microbial processes and long-term storage of environmental samples.

Keywords: biogeochemical processes; deep sea; hydrostatic pressure; piezophile; sulfate reduction.

Figure 1

Model of the anaerobic food web coupled to sulfate as the terminal electron accepting process (after Jørgensen, 2006) for the Japan Trench sediments. Detrital organic matter is buried in the surface sediment as macromolecules (MM). During exoenzymatic hydrolysis macromolecules are broken down to low molecular weight molecules (LMW). Fermentation further degrades LMW to short chain fatty acids such as acetate, and hydrogen. Fluid seepage delivers additional methane to the near-surface sulfate-bearing sediments. Calyptogena colonies also thrive on methane seepage and chemosynthetic sulphide reducers. In addition to pressure, we manipulated concentrations of substrate methane, acetate and hydrogen (marked in bold) in order to tease out effects of pressure on the sulfate reducing community.

Figure 2

Bathymetric map of the Japan Trench showing the positions of Station 1 and 2.

Figure 3

Examples of bacterial T-RFLP electrophoretograms from Station 1 (upper profile) and Station 2 (lower profile). γ, δ and ε indicate the corresponding proteobacterial groups, and Sox and SRB indicate the sulfide oxidizing and sulfate reducing bacterial groups. The lengths of the fragments are displayed on the x-axis and relative fluorescence intensity of peaks is shown on the y-axis.

Figure 4

Examples of archaeal T-RFLP electrophoretograms from Station 1 (upper profile) and Station 2 (lower profile). MG-I, MET and ANME indicate the crenarchaeota marine group I, the methanogenic euryarchaeota group, and the anoxic methane oxidizing archaea group, respectively. The lengths of the fragments are displayed on the x-axis and relative fluorescence intensity of peaks is shown on the y-axis.

Figure 5

Extent of sulfate reduction over 29 days in sediment slurries from Station 1 (A,B) and Station 2 (C,D), stored at atmospheric pressure (A,C) and at in situ pressure (B,D) under organoclastic conditions, respectively. Incubations were conducted at atmospheric pressure (hollow square, median denoted as light grey horizontal bar) and high pressure (filled square, median denoted as black horizontal bar) and at 4°C, without addition of substrate (none) or amended with methane, acetate or hydrogen.

Figure 6

Extents of sulfate reduction in sediment slurries stored with a methane partial pressure of 0.2 MPa at (A) Station 1 and (B) Station 2. Incubations were conducted at atmospheric pressure (hollow square, median denoted as light grey bar) and in situ pressure (filled square, median denoted as black bar) and at 4°C, without addition of substrate (none) or amended with methane, acetate or hydrogen.