Application of ancient DNA to the reconstruction of past microbial assemblages and for the detection of toxic cyanobacteria in subtropical freshwater ecosystems

Ancient DNA (aDNA) analysis of lake sediments is a promising tool for detecting shifts in past microbial assemblages in response to changing environmental conditions. We examined sediment core samples from subtropical, freshwater Laguna Blanca (Uruguay), which has been severely affected by cultural eutrophication since 1960 and where cyanobacterial blooms, particularly those of the saxitoxin-producer Cylindrospermopsis raciborskii, have been reported since the 1990s. Samples corresponding to ~1846, 1852, 2000 and 2007 A.D. were selected to perform Denaturing Gradient Gel Electrophoresis (DGGE) analysis of the 16S-23S rRNA intergenic transcribed spacer (ribosomal ITS) to compare their prokaryotic assemblage composition. Each stratum showed different ITS patterns, but the composition of 21st Century samples was clearly different than those of mid-19th Century. This compositional change was correlated to shifts in sediment organic matter and chlorophyll a content, which were significantly ...