Benthic bacterial diversity along the Laptev Sea continental slope in the Arctic Ocean between two contrasting years (1993 and 2012)

Here we investigated differences in benthic bacterial community structure from surface sediments at the Laptev Sea continental slope between two contrasting years, 1993 and 2012. Samples were retrieved on two Polarstern expeditions sampling the same stations between 60 and 3400 m water depth: Polarstern expedition PS27 (ARK-IX/4) in 1993 and Polarstern expedition PS80 (ARK-XXVII/3) in 2012. Sampling was conducted with a multiple corer (MUC), in order to retrieve undisturbed sediment cores. Upon retrieval of the MUC, the overlying water was carefully removed from each core and the upper first centimeter of sediment was cut using a steel plate and a custom-made plastic ring. DNA was extracted from 1 g of sediment using the UltraClean Soil DNA Isolation Kits (MoBio Laboratories, USA) for samples from 1993 and from 0.5 g of sediment using the MoBio Power Soil Kit (MoBio Laboratories, USA) for samples from 2012, using the protocols provided by the manufacturer; DNA was eluted in 60-100 µl Tris-EDTA-buffer and stored at -20°C. 16S rRNA gene sequencing was accomplished with 454 pyrosequencing technology, using primers covering the hypervariable V4-V6 region (530F GTGCCAGCMGCNGCGG, 1100R GGGTTNCGNTCGTTR). Sequencing was performed on a 454 GS FLX machine at the Research and Testing Laboratory, Texas.