Jan 23, 2009

Research Projects

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Impacts of the cultivation of cyanophycin-producing potatoes on soil characteristics and soil organisms

(2008 – 2011) University of Trier

Topic

This project aims to investigate whether the cultivation of genetically modified potatoes that produce cyanophycin in their tubers alters the chemical characteristics of the soil and the composition of the micro-organism communities in the soil. Cyanophycin is a biopolymer that is used for various industrial applications.

In nature the protein cyanophycin is produced by blue-green algae and therefore does not normally occur in arable soil. In the genetically modified potato it is stored at the expense of the carbohydrates that are so abundant in the tuber. The breakdown of cyanophycin in the soil is likely to promote other micro-organisms than those promoted during the breakdown of carbohydrates.

The main key organisms in Central European soils, the earthworms, may also react to cyanophycin.

Cyanophycin-producing potatoes also contain more peroxidases than the wild type. These are [L:enzymes]] that protect the plants against attack by micro-organisms – organisms that play a considerable part in humus formation in the soil. The higher level of peroxidases could make the transgenic potatoes rot more slowly. It could also lead to changes in humus formation.

This project will examine the following questions:

• How does the microbial breakdown of cyanophycin-producing potatoes in the soil compare with that of wild type potatoes?
• Does the cultivation of cyanophycin-producing potatoes alter the chemical characteristics of the soil and the composition of the micro-organism community in the soil?
• Are there any identifiable impacts on earthworms?

Experiment description

Microbial breakdown of cyanophycin-producing potatoes compared with wild type potatoes

For this part of the project a detection method for cyanophycin first has to be developed. Chromatographic methods will be used in which chemical substances are separated by size and identified.

The microbial breakdown of the potatoes will be investigated in the laboratory. The same volumes of transgenic potatoes and wild type potatoes will be placed in soil and will remain there under controlled conditions (temperature, humidity) for several months. Samples will be taken from the rotting potatoes at five points in time and the dry matter and ash content will be measured. To determine the ash content, potato tissue is burnt at 500°C and the residue is weighed. The ash content increases the higher the level of decomposition, based on the dry weight of the tissue, so is a measure of the advancing breakdown of the potatoes.

In the first four weeks, when the microbial activity is at its peak, the release of CO2 is measured constantly because it provides an indication of the microbial conversion rate. The cyanophycin level in the soil is also measured regularly.

Soil characteristics and composition of the micro-organism community in the soil

In the release experiments, which are designed to last several years, soil samples will be taken six times in every growing season. These will be tested for selected soil chemical parameters, such as pH value, and tests will also be carried out to investigate the biomass of the micro-organisms from the rhizosphere and the activity of certain bacterial enzymes.

In addition, genetic profiles will be produced. In these, individual genes are examined that are present in all species of bacteria but which are known to display species-specific differences in terms of their DNA sequence.

The soil chemical and microbiological tests will also be conducted on the laboratory batches (see above) to verify the results of the field trials.

Impacts on earthworms

The reaction of earthworms to the cultivation of cyanophycin-producing potatoes will be determined using e.g. activity tests and excrement levels.