Cyanophycin potatoes

Plastic from potatoes

A field trial at the University of Rostock is developing methods for assessing the safety of 2nd and 3rd generation GM plants long before they are potentially brought onto the market. One prototype for such plants is a potato that has been genetically modified so that its tubers and leaves produce cyanophycin, which can be used to obtain a biodegradable plastic. Two current biosafety research projects are studying the potential environmental impacts of cyanophycin potatoes.

Trial field with genetically modified potatoes

right: cyanophycin potato plant; left: parent variety

Cyanophycin in the cells of potato tubers

Photo taken using electron microscope, 28,500 x magnification

Cyanophycin is a protein produced by cyanobacteria (blue-green algae) and some other bacteria. They use it to store nitrogen, among other things. One component of cyanophycin is polyaspartate, which can be used as a biodegradable plastic. Polyaspartate binds calcium and therefore has potential applications in e.g. detergents as a water softener.

It is possible to produce such biodegradable polymers (biopolymers) in plants, using the plant as a kind of bioreactor. Plants could therefore act as renewable raw materials supplying substitutes for petroleum-based plastics that are not biodegradable, e.g. acrylic-acid-based polyacrylates.

Polyaspartate can also be obtained through chemical synthesis, but is currently produced only in small quantities. It is more biodegradable than comparable polyacrylates, but not totally biodegradable like the polyaspartate produced in cyanophycin.

Cyanophycin has another valuable component: the amino acid arginine, which improves animal health when added to feed and reduces the level of nitrogen in urine.

As well as producing cyanophycin in plants, it is possible to produce it in bioreactors (fermenters) using biotechnology methods with bacteria or cell cultures. However, this produces genetically modified bacteria like GM E.coli bacteria, instead of cyanobacteria. An advantage of producing cyanophycin in plants instead of in fermenters is that cyanophycin can be produced cheaply as a by-product. Potatoes grown for starch production can be used to produce cyanophycin at the same time. No additional fields would be needed.

Years of research

Researchers have been studying the production of cyanophycin in plants for years. In a joint project funded by the German Federal Ministry of Food, Agriculture and Consumer Protection (BMELV), scientists at the Universities of Rostock, Berlin, Bielefeld and Tübingen have developed cyanophycin potatoes and examined them in detail in the greenhouse.

A gene from the cyanobacterium Thermosynechoccus elongatus was transferred into the potatoes, resulting in production of a special enzyme: a cyanophycin synthetase. This enzyme causes cyanophycin to be produced from the amino acids aspartate and arginine in the potato plant. Aspartate and arginine are converted into the long-chain molecule polyaspartate with arginine residues.

The potatoes have been optimised over many years so that they can produce large quantities of cyanophycin in their tubers without impairing the fitness of the plants.

Researchers are also investigating possible procedures for extracting the cyanophycin cheaply from the potatoes. The trials show that even simple procedures are capable of extracting up to 80% pure cyanophycin as a white powder. It accounts for as much as 6% of the dry weight of the potatoes.

Field trials

Now researchers are using the potatoes as a model plant to test in the field to what extent plants can be used as safe production systems for bioplastics. The team is testing whether field conditions affect production and whether there are any effects on [[L:8|non-target organisms]]. The tubers are also being used for feeding experiments to test for potential allergenic or toxic effects. The researchers will test potato plants that produce cyanophycin in all parts of the plant as well as those that produce it only in the tuber.

Two of the research projects funded by the German Federal Ministry of Education and Research (BMBF) are also studying cyanophycin potatoes. One of the projects is investigating whether the genetic modification causes unintended changes to the characteristics of the potato. If, for instance, the potato is less sensitive to frost, potatoes left on the field would be more likely to survive the winter. In addition, the scientists are testing whether the rotting process is any different.

Another project is looking at microbial breakdown in the soil of plant remains left on the field and possible changes to the community of micro-organisms.

In June 2006 the Federal Office of Consumer Protection and Food Safety (BVL) authorised the 2006-2008 field trials on condition that precautionary measures are taken. These included locating the trial field at least 150 metres from other potatoes, fencing it off to prevent wild animals eating or carrying off potatoes, and inspecting the field after the end of the trial for any potatoes that might have survived.

More release applications have been submitted for the years up to 2012.