Genetic diversity in green algae (Hydrodictyaceae) obtained from modern and ancient sedimentary DNA of Siberian lakes

• Main Author: Lütje, Jan
• Format: Thesis
• Language: unknown
• Published: 2014
• Subjects: Arctic; Tundra; Siberia
• Online Access: https://epic.awi.de/id/eprint/42126/; https://epic.awi.de/id/eprint/42126/1/Bachelorarbeit_Jan_Luetje_PDF.pdf; https://hdl.handle.net/10013/epic.48983; https://hdl.handle.net/10013/epic.48983.d001

Pediastrum and other representatives of the green algae family Hydrodictyaceae (Chlorophyta), commonly found in freshwater environments, are potential bioindicators for paleolimnological studies as they are preserved in sediments and morphologically classified as non-pollen palynomorphs obtained along with pollen spectra. The aim of this study was to examine the diversity in Hydrodictyaceae obtained from modern and ancient Siberian lake sediments following a molecular genetic approach. Environmental samples were obtained from lakes across the arctic-boreal tree line in Siberia. Modern sedimentary DNA (sedDNA) was isolated from the samples and a selected fragment of the rbcL gene, encoding the large subunit of the enzyme RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase), was amplified via polymerase chain reaction (PCR). The respective primer pairs were specifically developed beforehand and optimized for the desired target fragment in Hydrodictyaceae. Four primer combinations were tested on two modern sediment samples and the most suitable primer combination was selected and applied to additional modern and core samples. The PCR products were cloned and sequenced by Sanger sequencing; the sequences were aligned and verified and taxonomic identification was conducted based on BLAST nucleotide search. 71.2 % of the obtained sequences were assigned to Hydrodictyaceae in ten out of eleven samples and 28.8 % to unknown algae strains in nine out of eleven samples. In total, thirteen different rbcL lineages were detected, among them twelve lineages of Pediastrum and Pseudopediastrum in modern sediments and six in ancient core sediments, including a single Stauridium lineage in one core sample. Five different lineages were detected in both sample types. One sample did not yield any Hydrodictyaceae lineage. Although the preliminary results of this study indicated that the distribution of lineages was fairly heterogeneous, we recognized a general tendency in terms of sample type (surface/core) and vegetation type (tundra/forest tundra/forest), but could not identify distinct preferences of single lineages. Phylogenetic inferences of the lineages indicated that a resolution down to species and strain level is not possible for most of the examined lineages. However, this study showed that Pediastrum DNA was reliably amplified from modern lake sediments and from core depths of up to 62 cm, the latter of which yielded ancient DNA (aDNA) with an age of approximately 3000 years. Possibly further studies covering larger datasets and additional genetic markers will give better resolution in terms of quantification, taxonomic coverage and identification.