Branched GDGT Production at Elevated Temperatures in Anaerobic Soil Microcosm Incubations


Yufei Chen, Fengfeng Zheng, Songze Chen, Haodong Liu, Tommy J. Phelps, Chuanlun Zhang


Branched glycerol dialkyl glycerol tetraethers (bGDGTs) are unique ether-linked bacterial membrane lipids, which occur in diverse environments. Acidobacteria are considered to produce them in acidic soils and peat bogs. However, the biological source(s) of bGDGTs other than acidobacteria in alkaline soils and their response to environmental changes are obscure. We designed a 1 year incubation experiment under elevated temperature conditions (30 °C, 45 °C and 85 °C) in order to accelerate the growth of mesophilic and thermophilic bacteria that may potentially produce bGDGTs and to understand the mechanisms underlying the changes in bGDGT composition. The soil we selected was alkaline (pH > 8) with a small population of acidobacteria being detected using high throughput sequencing. The medium contained nutrients and organic carbon and samples were incubated under anaerobic conditions with pH of 7.5, in order to stimulate the growth of heterotrophic and anaerobic bacteria from the soil. Quantitative polymerase chain reaction (qPCR) was employed to monitor the growth status of bacteria at the beginning and the end of the experiment. The results showed multiple lines of evidence for bGDGT biosynthesis, including: (1) increased total abundance of both PL-bGDGTs (polar lipid-derived bGDGTs, “living”) and CL-bGDGTs (core lipid bGDGTs, “dead”) at 30 °C and 45 °C, but not 85 °C; (2) changes in bGDGT distribution at 30 °C and 45 °C; and (3) increased temperature inferred by the bGDGT-based proxy at an incubation temperature at 45 °C. Estimated turnover time of both PL- and CL-bGDGTs was 1–8 months at 30 °C or 45 °C under these laboratory conditions, which agrees with previous studies. Our study suggests that raising temperature may stimulate growth of bGDGT-producing bacteria that likely includes some anaerobic heterotrophs other than acidobacteria.

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Chen YF, Zheng FF, Chen SZ, Liu HD, Phelps TJ, Zhang CL. 2018. Branched GDGT production at elevated temperatures in anaerobic soil microcosm incubations. Organic Geochemistry 117:12-21.