Prof. Dr. Ulrich Szewzyk, PD Dr. Elisabeth Grohmann
In the second period of the project we focus on the influence of microbial communities on soil texture and dynamics of organic matter. The main emphasis will be put on investigations with regard to the impact of microorganisms on water repellence of urban soil and microbial immobilization and mobilization of soil components and organic pollutants. The research topics are:
i. characterization of the active microbial communities with regard to biotransformations in soil transformation of organic pollutants (subproject MOBIL)
ii. adsorption characteristics of microorganisms to soil particles microbial impact on development of hydrophilic and hydrophobic areas (subproject HUMUS)
ad i. Analyses of microbial communities active in degradation of organic pollutants characteristic for the sampling site sewage field Berlin Buch will be performed by stable-isotope probing (SIP). For selected bacterial degraders FISH probes will be designed to prove their presence in situ and to localize them in the urban habitat.
ad ii) Two different reactor types will be used to produce abundant microbial biomass for interdisciplinary investigations.
Homogenous biofilms will be grown in upflow fixed bed reactors. To simulate conditions at the sampling sites downstream percolation reactors periodically fed with medium will be set up. The microorganisms in this reactor system will be exposed to various periods of water and heat stress.
Samples from the percolation reactor will be analysed to determine the sorption kinetics of
These experiments shall help to define the microbial influence on development of hydrophobic and hydrophilic areas in anthropogenic soils.
Prof. Dr. Ulrich Szewzyk, PD Dr. Elisabeth Grohmann
Biofilms and bacterial aggregates play an important role for the structure and physico-chemical features of soil. Not only the physiological and metabolic activities of microorganisms but also their influence on soil matrix properties is essential. Most important features are rigidity of soil particles, crumbliness and the ability to retain water. Macromolecular structures such as slimes (polysaccharides and proteins), probably together with humic substances, are responsible for these soil characteristics. The slimes (extracellular polymeric substances = EPS) are mainly produced by microorganisms and various soil invertebrates.
We aim to analyze structure and density as well as importance of microbial biofilms for water and matter fluxes in urban soils. With regard to dryness, contaminants (pollutants) and salt concentration urban soils often represent extreme habitats forcing the colonizing flora to adapt to these extreme conditions. Microbial protection mechanisms are provided by gradients, formed by the three dimensionally organized biofilms and their associated EPS structures. High amounts of EPS shelter the enclosed bacteria and prevent them from drying up, as was demonstrated for desert colonizing cyanobacteria. The sampling sites are an urban park (Berliner Tiergarten) and a sewage farm (Rieselfeld) as a Berlin peculiarity.
To analyze the distribution of predominant bacterial groups depth profiles of different sampling sites are analyzed by fluorescence in situ hybridization (FISH). On the molecular level microbial diversity dependent on soil depth and humidity is being studied by ARDRA (amplified rDNA restriction analysis) and DGGE (denaturing gradient gel electrophoresis). Soil samples from various sampling sites are applied to cultivation on special media to establish a collection of urban soil isolates for further investigations. The isolates are tested for hydrophobicity, production of secondary metabolites and signal molecules and are being applied to interdisciplinary laboratory experiments in soil microcosms and biofilm reactors.
Intensive collaboration and data exchange with the project partners will help correlate the presence of biofilms (in association with EPS) with the physico-chemical parameters determined by the project partners for the urban sampling sites.
Dr. Elisabeth Grohmann
Dr. Uta Böckelmann
Burga Braun
Katharina Knobel