Temperature and pH controls on glycerol dibiphytanyl glycerol tetraether lipid composition in the hyperthermophilic crenarchaeon Acidilobus sulfurireducens
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Cyclization in glycerol dibiphytanyl glycerol tetraethers (GDGTs) results in internal cyclopentane moieties which are believed to confer thermal stability to crenarchaeal membranes. While the average number of rings per GDGT lipid (ring index) is positively correlated with temperature in many temperate environments, poor correlations are often observed in geothermal environments, suggesting that additional parameters may influence GDGT core lipid composition in these systems. However, the physical and chemical parameters likely to influence GDGT cyclization which are often difficult to decouple in geothermal systems, making it challenging to assess their influence on lipid composition. In the present study, the influence of temperature (range 65–81°C), pH (range 3.0–5.0), and ionic strength (range 10.1–55.7 mM) on GDGT core lipid composition was examined in the hyperthermoacidophile Acidilobus sulfurireducens, a crenarchaeon originally isolated from a geothermal spring in Yellowstone National Park, Wyoming. When cultivated under defined laboratory conditions, the composition of individual and total GDGTs varied significantly with temperature and to a lesser extent with the pH of the growth medium. Ionic strength over the range of values tested did not influence GDGT composition. The GDGT core lipid ring index was positively correlated with temperature and negatively correlated with pH, suggesting that A. sulfurireducens responds to increasing temperature and acidity by increasing the number of cyclopentyl rings in GDGT core membrane lipids.
KeywordsGlycerol dibiphytanyl glycerol tetraether GDGT Yellowstone pH Temperature Crenarchaea
This research was supported by National Science Foundation grant MCB-0132022 to GGG and National Science Foundation grant MCB-0348180 to CLZ with subcontract award to AP. CLZ was also supported by the National Natural Science Foundation of China (Award # 40972211) and the State Key Laboratory of Marine Geology at Tongji University. ESB acknowledges support from the Inland Northwest Research Alliance and the NASA Astrobiology Institute postdoctoral fellowship program.
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