Quantification of endospores in ancient permafrost using time-resolved terbium luminescence

We describe herein a simple procedure for quantifying endospore abundances in ancient and organic-rich permafrost. We repeatedly (10x) extracted and fractionated permafrost using a tandem filter assembly composed of 3 and 0.2 mu m filters. Then, the 0.2 mu m filter was washed (7x), autoclaved, and the contents eluted, including dipicolinic acid (DPA). Time-resolved luminescence using Tb(EDTA) yielded a LOD of 1.46 nM DPA (6.55 x 10(3) endospores/mL). In review, DPA/endospore abundances were similar to 2.2-fold greater in older 33 ky permafrost (258 +/- 36 pmol DPA gdw(-1); 1.15 x 10(6) +/- 0.16 x 10(6) spores gdw(-1)) versus younger 19 ky permafrost (p = 0.007297). This suggests that dormancy increases with permafrost age.