DNA from lake sediments reveals the long-term dynamics and diversity of Synechococcus assemblages

[摘要] While picocyanobacteria (PC) are important actors in carbon and nutrientcycles in aquatic systems, factors controlling their interannual dynamicsand diversity are poorly known due to the general lack of long-termmonitoring surveys. This study intended to fill this gap by applying aDNA-based paleolimnological approach to sediment records from a deepsubalpine lake that has experienced dramatic changes in environmentalconditions during the last century (eutrophication, re-oligotrophication andlarge-scale climate changes). In particular, we investigated the long-term(100 yr) diversity and dynamics of Synechococcus,, PC that have presumably been affectedby both the lake trophic status changes and global warming.The lake's morphological and environmental conditions provided the idealconditions for DNA preservation in the sediment archives. Generalisedadditive models applied to quantitative PCR (qPCR; quantitative Polymerase Chain Reaction) results highlighted thatan increase in summer temperature could have a significant positive impacton the relative abundance of Synechococcus, (fraction of Synechococcus, in total cyanobacteria).The diversity of Synechococcus, in Lake Bourget was studied by phylogenetic analyses ofthe 16S rRNA gene and the following internally transcribed spacer (ITS). Upto 23 different OTUs (based on 16S rRNA), which fell into variouscosmopolitan or endemic clusters, were identified in samples from the past100 yr. Moreover, the study of ITS revealed a higher diversity within themajor 16S rRNA-defined OTUs. Changes in PC diversity were related to thelake's trophic status. Overall, qPCR and sequencing results showed thatenvironmental changes (in temperature and phosphorus concentration)affected Synechococcus, community dynamics and structure, translating into changes ingenotype composition. These results also helped to re-evaluate thegeographical distribution of some Synechococcus, clusters.Providing such novel insights into the long-term history of an importantgroup of primary producers, this study illustrates the promising approachthat consists in coupling molecular tools and paleolimnology to reconstructa lake's biodiversity history.

[学科分类] 地球化学与岩石