Metatranscriptomes obtained from AFISsys prototype 1, AFIS and free-flow bottles, over 24 hours

Microbial genes and transcripts principally mirror most metabolic pathways by which elements are transformed, as well as physiological adaptations (e.g., to stressors), and thus provide snapshots of the environmental status of a system. The presence of abundant transcripts can be used as immediate and sensitive markers for contemporary environmental conditions and the occurrence of certain stress conditions that may alter biogeochemical pathways. Thus, environmental assessment of ecological status and its monitoring may be dramatically improved using metatranscriptomic approaches directed at prokaryotic microbes. Through the development of the autonomous in situ fixation multi-sampler AFISsys, the AFISmon project intended to provide the basis for the generation of high-resolution and non-biased functional microbial genetic profiles. A field test of the first AFISsys prototype was conducted in the Warnow River, at the Baltic Taucherei pier in Rostock, Germany. As this test was conducted in the end of September 2016, the daylight cycle was equally distributed between 12 hours of sunlight and 12 hours of darkness. With 3-hour intervals we were able to capture sunset and sunrise, with an additional 4 time points during the day and 3 at night. As the multisampler prototype was made up of three individual sampling modules, this constituted 3 sampling times after which the prototype was taken out of the water and the samples were collected and filtered. The prototype was then reset (springs were sprung, modules clipped back onto the rack) and redeployed to the same depth, for the next three sampling points. In parallel to the AFISsys samples, we collected water with the original IOW AFIS (see Feike et al., 2012. ISME Journal) and with a standard free-flow HydroBios bottle. Both samplers were fitted onto a rod with a mechanical closing system to allow manual operation without the need for a rosette or winch. These AFIS and free-flow samples constituted reference samples, for a fixed reference and an unfixed reference, to establish the quality of the samples taken with the AFISsys. Furthermore, in the event that the prototype should not function as expected, the reference samples would permit us to still pursue our Eulerian study of microbial activity.