The detritusphere as biogeochemical interface for bacterial and fungal degradation of MCPA and phenanthrene

Principle investigators: Prof. Dr. E. Kandeler, Prof. Dr. T. Streck

Co-workers: Dr. J. Ingwersen, Dr. C. Poll, Dipl.-Ing. H. Pagel

This project aims to clarify microbiological and physicochemical interactions during the degradation of 2-methyl-4-chlorophenoxyacetic acid (MCPA) and phenanthrene in the detritusphere. The detritusphere offers a unique opportunity to study metabolism and co-metabolism by a bacterial and fungal community along a gradient of decreasing availability of low molecular weight substances within a distance of 10 mm from the soil-litter interface. First, we will estimate the MCPA and phenanthrene degrading genetic potential by quantitative PCR of functional genes. Second, we will clarify the fungal and bacterial contribution to degradation by tracing the carbon flow into fungal and bacterial derived 13C PLFAs and 13C ergosterol. Third, we will combine 13C/14C techniques to elucidate the time-dependent interplay between biological and physical processes during degradation. Fourth, we will model transport and degradation of MCPA and phenanthrene as well as small-scale microbial growth using, for the first time, abundances of functional genes. The project will be carried out in close collaboration between the soil biology group (Prof. E. Kandeler) and the biogeophysics group (Prof. T. Streck) of the Institute of Soil Science and Land Evaluation (University of Hohenheim) as well as an external partner from France (Dr. Fabrice Martin-Laurent) of the Laboratory of Soil Microbiology and Geochemistry (INRA, Dijon).

Goals
• Localise functional genes involved in degradation of MCPA and phenanthrene in the detritusphere
• Assess the carbon flow through an MCPA degrading bacterial and fungal community in the detritusphere
• Elucidate the time-dependent interplay between biological (metabolism, co-metabolism) and physical (adsorption, desorption and transport) processes during the degradation of MCPA and phenanthrene in the detritusphere
• Model small-scale microbial growth, degradation, and transport of MCPA and phenanthrene near the soil-litter interface based on measured densities of functional genes and physico-chemical properties of the chemicals under study
Hypotheses
• The inflow of low-molecular substances causes the metabolic/ cometabolic degradation of MCPA and phenanthrene
• Bacteria and fungi show different utilisation strategies of MCPA and phenanthrene in the detritusphere
• These processes depend on physicochemical properties of MCPA and phenanthrene as well as the transport of low molecular organic substances

Scientific approach
We plan to combine microbial and physicochemical analytics with mathematical modelling. For the very first time the abundance of functional genes serves as a basis for modelling the microbial degradation of MCPA and phenanthrene. Furthermore, we will use 13C and 14C labelled substances or litter to trace the C transport and incorporation into the microbial biomass.
We will perform three main experiments using microcosms. These microcosms offer the possibility to study transport conditions in the detritusphere by adjusting water contents via ceramic plates. For modelling, we will use the data of the three main experiments and the data of side experiments that we will carry out to independently estimate some of the model parameters.
• The first experiment will focus on bacterial and fungal degradation of MCPA and phenanthrene in the detritusphere by quantifying and localising functional genes involved in the degradation of MCPA and phenanthrene
• In the second experiment, we will trace the carbon flow through the MCPA and phenanthrene degrading community using 13C-PLFA and 13C-ergosterol
• In the third experiment, we will monitor the transport of low molecular weight substances from the litter into the detritusphere as well as their impact on the fate of MCPA and phenanthrene by coupling 13C and 14C isotope techniques
• We will set up a computer model to simulate the dynamics of the microbial and the MCPA and phenanthrene degrading community as well as the transport and degradation of MCPA and phenanthrene in the detritusphere.


Cooperations within the priority programme:
Prof. Dr. M. Kästner, Prof. Dr. Dr. h.c. M. Spiteller, Dr. M. Schloter, Prof. Dr. K. Smalla

Publications:
Poll, C., Pagel, H., Devers-Lamrani, M., Martin-Laurent, F., Ingwersen, J., Streck, T., Kandeler, E. 2010. Regulation of bacterial and fungal MCPA degradation at the soil-litter interface. Soil Biol. Biochem. 42, 1879-1887.

Foto
Hohenheim1
Hohenheim2