Sedimentary membrane lipids recycled by deep-sea benthic archaea

Abstract

Deep-sea sediments harbour a vast biosphere. Archaea—one of the three domains of life1—are prevalent in marine environments2, 3, 4, 5, and comprise a significant fraction of the biomass in marine sediments6. Archaeal membranes are well characterized, and are comprised of a glycerol backbone and a nonpolar isoprenoid chain. However, the ecology of sedimentary archaea remains elusive, because it is difficult to grow them in the laboratory. Here, we trace the fate of 13C-labelled glucose added to marine sediments in Sagami Bay, Japan, to determine the in situ mechanisms of membrane synthesis. Following the addition of labelled glucose to sediment samples collected in the region, we placed the cores on the sea floor and sampled them after 9 and 405 days. We found that the 13C was incorporated into the glycerol backbone of archaeal membranes; 13C was apparent after 9 days of incubation, but most pronounced after 405 days. However, the isoprenoid chain of the membranes remained unlabelled. On the basis of the differential uptake of 13C, we suggest that the glycerol unit is synthesized de novo, whereas the isoprenoid unit is synthesized from relic archaeal membranes and detritus, because of the prevalence of these compounds in marine sediments. We therefore suggest that some benthic archaea build their membranes by recycling sedimentary organic compounds

Archaea of the Miscellaneous Crenarchaeotal Group are abundant, diverse and widespread in marine sediments

“…MCG are likely to access substrates that are physically or chemically recalcitrant. This conclusion is in agreement with findings from previous literature (Biddle et al, 2006;Lipp et al, 2008;Takano et al, 2010;Webster et al, 2010;Lliró s et al, 2011).…”

Differing utilization of glucose and algal ­particulate organic matter by deep-sea benthic organisms of Sagami Bay, Japan

“…The present study focused on benthic foraminifera, because they are known to consume substantial amounts of organic carbon on the deep-sea floor (Moodley et al 2002, Gooday et al 2008). Total uptake rates of 13 C-labeled substrates by archaea were not quantified since (1) the archaeal biomass estimation based on the concentration of lipid biomarkers has some variables and (2) the rates of incorporation of 13 C to archaeal membrane lipids were highly heterogeneous between glycerol and isoprenoid (Takano et al 2010), making it difficult to estimate total archaeal uptake rate using a single membrane lipid biomarker. …”

“…com/articles/ suppl/ m431p011_supp.pdf). Subsamples (15 cm 3 ) of the sediments were used for the analysis of bulk organic matter and archaeal membrane lipid analysis (Takano et al 2010). These samples were kept frozen at -80°C and then freeze-dried.…”

Differential degradation of intact polar and core glycerol dialkyl glycerol tetraether lipids upon post-depositional oxidation

“…In situ production was suggested by Hoefs et al (2002), who found apparently high preservation efficiency of C 16 and C 18 fatty acids which was attributed, in part, to bacterial in situ production in the sediment. However, evidence has emerged that this in situ production of IPL-GDGTs may effectively be quite low (Takano et al, 2010;Lin et al, 2012;Xie et al, 2013), except for in settings with high activity such as sulfate-methane transition zones, and thus unlikely to cause a substantial change in IPL GDGT distributions.Here, we investigate the long-term (~10 kyr) effects of post-depositional oxygen exposure on the distribution of IPL GDGTs and CL GDGTs in the f-turbidite of the MAP (Buckley and Cranston, 1988). We analyzed CL GDGT and IPL GDGT concentrations and the respective TEX 86 , BIT and MBT/ CBT values of a fresh sediment core MAP-4 from the unoxidized f-turbidite, the overlying oxidized hemipelagic sediments, and the overlying unoxidized e-turbidite.…”