Fourier transform ion cyclotron resonance mass spectrometry analysis
All used instruments and software for the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) analysis were from Bruker Daltonik GmbH, Bremen, Germany. The measurements were performed on a solariX FT-ICR-MS with a 15 Tesla magnet system coupled with an Apollo II atmospheric pressure spray chamber. Negative electron spray ionization (ESI) mode was run for all samples.
The following parameters were set. Molecules occurred in less than 80 % of the samples were neglected. Only molecules with a mass to charge (m/z) ratio of 150 to 650 were considered. Allowed components within one molecule were: Cx; Hy; Oz<x; Ni<z; S1,2; P1( x, y, z, i = 1, 2, 3….). To avoid problems in the comparability between each single sample, everyone was standardized by the z-score method after the mentioned criteria were applied.
Results are indicated in van Krevelin Plots which are cross-plots of O/C and H/C ratios.
The 16S rRNA gene sequences of 60 samples from the mesocosms were amplified using 30 cycles with the primers Bakt_341F and Bakt_805R. The primers were complemented with sample-specific 5-bp barcodes and sequenced using Roche GS FLX titanium series chemistry.