Abstract
Microbial life in deep marine subsurface faces increasing temperatures and hydrostatic pressure with depth. In this study, we have examined growth characteristics and temperature-related adaptation of the Desulfovibrio indonesiensis strain P23 to the in situ pressure of 30 MPa. The strain originates from the deep subsurface of the eastern flank of the Juan de Fuca Ridge (IODP Site U1301). The organism was isolated at 20°C and atmospheric pressure from ~61°C-warm sediments approximately 5 m above the sediment–basement interface. In comparison to standard laboratory conditions (20°C and 0.1 MPa), faster growth was recorded when incubated at in situ pressure and high temperature (45°C), while cell filamentation was induced by further compression. The maximum growth temperature shifted from 48°C at atmospheric pressure to 50°C under high-pressure conditions. Complementary cellular lipid analyses revealed a two-step response of membrane viscosity to increasing temperature with an exchange of unsaturated by saturated fatty acids and subsequent change from branched to unbranched alkyl moieties. While temperature had a stronger effect on the degree of fatty acid saturation and restructuring of main phospholipids, pressure mainly affected branching and length of side chains. The simultaneous decrease of temperature and pressure to ambient laboratory conditions allowed the cultivation of our moderately thermophilic strain. This may in turn be one key to a successful isolation of microorganisms from the deep subsurface adapted to high temperature and pressure.
Highlights
The volume of world’s oceans 200 m below sea level constitutes more than 95% of all aquatic habitats (Michiels et al, 2008)
This was found for the type strain of D. indonesiensis (Ind1T), which had originally been isolated from a corroding ship at the sea surface (Feio et al, 1998)
Cultures of D. indonesiensis strain P23 grown at 45◦C revealed a cell length from 1–1.7 μm (±0.17 μm) at atmospheric pressure which increased to an average of 14.7 μm (±5.18 μm) at 40 MPa (n = 20)
Summary
The volume of world’s oceans 200 m below sea level constitutes more than 95% of all aquatic habitats (Michiels et al, 2008). Most studies to identify the microbial diversity within the deep marine subsurface are based on cultivation-independent approaches (Marchesi et al, 2001; Kormas et al, 2003; Inagaki et al, 2006; Webster et al, 2006; Biddle et al, 2008). Even though novel high-throughput techniques such as Piezophilic sulfate-reducing subsurface bacteria metagenomics or single cell genomics are important for predicting in situ ecological functions (Teske, 2006; Lauro and Bartlett, 2008), the isolation of microorganisms from deep ecosystems is seen as the “gold standard” to identify putative physiological capabilities and specific adaptation mechanisms (Giovannoni and Stingl, 2007) to subseafloor habitats. Isolates are still indispensable to verify metabolic pathways that are only detected by in silico analysis
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