Resurrection of a diatom after 7000 years from anoxic Baltic Sea sediment

Abstract

Dormancy is a widespread key life history trait observed across the tree of life. Many plankton species form dormant cell stages that accumulate in aquatic sediments and, under anoxic conditions, form chronological records of past species and population dynamics under changing environmental conditions. Here we report on the germination of a microscopic alga, the abundant marine diatom Skeletonema marinoi Sarno et Zigone, that had remained dormant for up to 6871 ± 140 years in anoxic sediments of the Baltic Sea and resumed growth when exposed to oxygen and light. Resurrected diatom strains, representing cohorts from six different time points of the past 6871 ± 140 years, are genetically differentiated, and fundamental physiological functions such as growth and photosynthesis have remained stable through time despite distinct environmental dynamics. Showing that resurrection and full functional recovery, in comparison to 3 ± 2 years of dormancy, is possible after millennial resting, we emphasize the relevance of dormancy and living sediment archives. For the future, sediment archives, together with the resurrection approach, would offer a powerful tool to trace adaptive traits over millennia under distinct climatic conditions and elucidate the underlying mechanisms.

Keywords: Skeletonema; dormancy; phytoplankton; resurrection; traits.

Figure 1

Location of sediment sampling and pictures of resurrected species S. marinoi. (A) Map of the Baltic Sea (northern Europe) with the location of sediment core sampling (EMB262/6; 240 m water depth) in the eastern Gotland Basin (triangle). Additional sampling points of stratigraphy reference cores (points): M86-1a/36 [35], MSM62–60 [36], and P435-2-1 [34]. (B) Pictures of different Lugol-stained strains of S. marinoi. Strain SM_EGB_382_11 from 6871 ± 140 years of dormancy, SM_EGB_1_5 from 3 ± 2 years of dormancy, SM_EGB_107_1 from 1131 ± 110 years of dormancy, SM_EGB_20_4 from 58 ± 5 years of dormancy, and SM_EGB_232_2 from 3411 ± 120 years of dormancy. Scale bars = 20 μm.

Figure 2

Age-depth model of core EGB262/6 from the eastern Gotland Basin with the age of resurrected temporal cohorts of S. marinoi (triangles). The Br/K ratio of the sediments reflects the relative organic matter content of the sediment [60], with high (low) Br/K values indicating high (low) contents. Calculated years ± root mean squared errors. Years in (calculated years) BP (before present = 1950) and B/CE (before the/common era) respectively.

Figure 3

(A) Mean growth rate of S. marinoi temporal cohorts from 3 ± 2 (n = 4), 58 ± 5 (n = 4), 181 ± 15 (n = 4), 1131 ± 110 (n = 7), 3411 ± 120 (n = 3), and 6871 ± 140 (n = 8) years of dormancy at 4°C. (B) Mean oxygen production of S. marinoi temporal cohorts from -3 ± 2 (n = 3), 1131 ± 110 (n = 4), 3411 ± 120 (n = 3), and 6871 ± 140 (n = 4) years of dormancy at 4°C.