ALBERT

Description: The concept of a ‘plastisphere microbial community’ arose from research on aquatic plastic debris, while the effect of plastics on microbial communities in soils remains poorly understood. Therefore, we examined the inhabiting microbial communities of two plastic debris ecosystems with regard to their diversity and composition relative to plastic-free soils from the same area using 16S rRNA amplicon sequencing. Furthermore, we studied the plastic-colonizing potential of bacteria originating from both study sites as a measure of surface adhesion to UV-weathered polyethylene (PE) using high-magnification field emission scanning electron microscopy (FESEM). The high plastic content of the soils was associated with a reduced alpha diversity and a significantly different structure of the microbial communities. The presence of plastic debris in soils did not specifically enrich bacteria known to degrade plastic, as suggested by earlier studies, but rather shifted the microbial community towards highly abundant autotrophic bacteria potentially tolerant to hydrophobic environments and known to be important for biocrust formation. The bacterial inoculates from both sites formed dense biofilms on the surface and in micrometer-scale surface cracks of the UV-weathered PE chips after 100 days of in vitro incubation with visible threadlike EPS structures and cross-connections enabling surface adhesion. High-resolution FESEM imaging further indicates that the microbial colonization catalyzed some of the surface degradation of PE. In essence, this study suggests the concept of a ‘terrestrial plastisphere’ as a diverse consortium of microorganisms including autotrophs and other pioneering species paving the way for those members of the consortium that may eventually break down the plastic compounds.

Description: Sedimentary ancient DNA-based studies have been used to probe centuries of climate and environmental changes and how they affected cyanobacterial assemblages in temperate lakes. Due to cyanobacteria containing potential bloom-forming and toxin-producing taxa, their approximate reconstruction from sediments is crucial, especially in lakes lacking long-term monitoring data. To extend the resolution of sediment record interpretation, we used high-throughput sequencing, amplicon sequence variant (ASV) analysis, and quantitative PCR to compare pelagic cyanobacterial composition to that in sediment traps (collected monthly) and surface sediments in Lake Tiefer See. Cyanobacterial composition, species richness, and evenness was not significantly different among the pelagic depths, sediment traps and surface sediments (p 〉 0.05), indicating that the cyanobacteria in the sediments reflected the cyanobacterial assemblage in the water column. However, total cyanobacterial abundances (qPCR) decreased from the metalimnion down the water column. The aggregate-forming (Aphanizomenon) and colony-forming taxa (Snowella) showed pronounced sedimentation. In contrast, Planktothrix was only very poorly represented in sediment traps (meta- and hypolimnion) and surface sediments, despite its highest relative abundance at the thermocline (10 m water depth) during periods of lake stratification (May–October). We conclude that this skewed representation in taxonomic abundances reflects taphonomic processes, which should be considered in future DNA-based paleolimnological investigations.

Description: This work was integrated into the Russian-German joint venture project System Laptev Sea 2000. The focus of this project was to extent our knowledge about the Laptev Sea system in north-east Siberia obtained through previous Russian-German projects, such as the Laptev Sea System (1994-1997), and Taymyr (1994-1997). Studies on Quaternary environmental changes, Arctic coastal dynamics and recent periglacial processes including ecological studies on permafrost soils and ecosystems of the central Lena Delta were in the focus of the recent project (Schirrmeister et al., 2004). The present work contributes to the last aspect by investigating the field of methane fluxes in polygonal tundra environments of the Lena Delta. Field work and sampling of this study was conducted during the expeditions LENA 2002 and LENA 2005 (Samoylov Island, Lena Delta, Siberia) with a personal participation in the last expedition. The work was performed in the frame of the International Max Planck Research School for Marine Microbiology (MarMic) mainly at the Alfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam. Some analyses were conducted at the Max Planck Institute for Marine Microbiology in Bremen. This study is presented in English as a cumulative Ph.D. thesis at the University of Bremen (Fachbereich 02). The thesis consists of a general introduction to the particular research field including the scientific background as well as aims and objectives of this study. The study area is described in an extra chapter. The main part of this thesis consists of three manuscripts with first authorship and a final synthesis representing the conclusions as well as critical remarks and future prospects of this work.