Deep-sea hydrothermal vents are unique environments, which are thought to represent models for both the origin of life on Earth and exploration of life on other planets. These vents contain ecosystems, which are predominantly fueled by geochemical energy and are host to many newly described free-living microbes, which are often associated with actively venting porous deep-sea vent deposits or “chimneys”. The steep chemical and thermal gradients within the walls of these deposits provide a wide range of microhabitats for microorganisms with suitable conditions for aerobic and anaerobic thermophiles and mesophiles (e.g. McCollom and Schock 1997
). Indeed, both culture-dependent and -independent approaches have exposed a vast diversity of Bacteria and Archaea associated with deep-sea vent deposits (e.g. Reysenbach and Shock 2002
; Schrenk et al. 2003
). Numerous Archaea have been isolated from these deposits but few of these are found in environmental 16S rRNA gene clone libraries and most detected environmental clones in these environments have no representatives available in pure culture.
In particular, one archaeal lineage is widespread at deep-sea vents, namely the “deep-sea hydrothermal vent euryarchaeotic” lineage DHVE2, and is frequently associated with actively venting sulphide deposits (e.g. Nercessian et al. 2003
; Hoek et al. 2003
; Reysenbach and Shock 2002
; Takai et al. 1999
). In some cases it has been reported as the most dominant clone type in archaeal clone libraries (Hoek et al. 2003
), yet the physiology of these organisms was unclear. Recently, Reysenbach et al. (2006
) isolated and cultivated a member of the DHVE2 phylogenetic DHVE2 cluster, Candidatus “Aciduliprofundum boonei
”, and showed it to be an obligate thermoacidophilic sulphur and iron reducing heterotroph capable of growing from pH 3.3 to 5.8 and between 60 and 75°C. This provided the first evidence that thermoacidophiles may be key players in sulphur and iron cycling at deep-sea vents.
Archaea are not only unique in their 16S rRNA phylogenetic position in the tree of life, but also synthesize specific membrane lipids. Analysis of cultivated hyperthermophilic Archaea showed that their membrane is predominantly composed of isoprenoid glycerol dibiphytanyl glycerol tetraethers (GDGTs) with additional cyclopentyl moieties (e.g. Structures I–VI in Fig. ). The structural differences from diacyl membrane lipids of non-thermophilic Eukarya and Bacteria, i.e. ether bonds and the formation of a monolayer rather than a bilayer, have been suggested to contribute to the stability of membranes of hyperthermophiles at high temperatures and low pH (e.g. De Rosa and Gambacorta 1988
; van den Vossenberg et al. 1998
; Macalady et al. 2004
). This suggests that members of the DHVE2 cluster may be also synthesizing GDGT membrane lipids. Therefore, in this study we analyzed the lipid composition of the only cultivated representative of DHVE2, Aciduliprofundum boonei
, and examined both the core GDGT lipid composition as well as its intact polar lipid composition.
Fig. 1 HPLC/APCI/MS base peak chromatogram of GDGT core lipids in extract released after base hydrolysis (using KOH/methanol mixture) of the cell material of Candidatus “Aciduliprofundum boonei”. Inset shows the atmospheric pressure chemical (more ...)