Scientists aim to create bacteria "mini factories," using microorganisms to produce new materials for industrial use
When engineers detect new biological design principles, they usually try to translate them into new technologies – and ultimately novel applications. But this unfolding of innovation doesn't only happen on a large scale: micro and nano-structured biomaterials are becoming the new source-of-choice for industrial materials.
"Natural materials are ingeniously structured composites that combine many interesting qualities," says Joachim Bill, materials scientist at the University of Stuttgart. "Take for example mother of pearl shells. They are especially hard, firm and yet extremely durable. Such substances, which follow biological structures, are technically versatile."
Under the microscope, the mother of pearl's secrets are quickly revealed: the substance is composed of many layers of a particular form of crystalline calcium carbonate. In each layer, tiny hexagonal crystals of aragonite overlap like tiles, and a thin layer of organic glue holds the individual layers together. "Because of this structure, shells are 3,000 times more durable than pure aragonite" says Bill.
His research team has developed a kind of artificial pearl based on titanium dioxide. This material, which is bionic-inspired and extremely scratch-resistant, can be applied to plastic surfaces. "A well-known bathtub manufacturer is even looking to apply this technology to its products," says Bill. At the moment, however, it remains in preliminary research phases.
Natural biomaterials have little industrial application – for this reason, the team is working to change the genes responsible for bio-materialization. By doing this, they hope to be able to control the shape, size and chemical composition of their materials. The German Research Foundation supports this research with about two million euros annually. The materials scientists, who are working together with three other institutions, are expected to produce results within six years.
The Stuttgart team is currently working to create special oxide ceramic from viruses. Specifically, they want zinc oxide, which is used to develop transparent electrically conductive layers that serve as contacts for light emitting diodes, solar cells and liquid crystal displays. Zinc is an essential trace element in living organisms, and has many biological functions. "We want to change the genetic regulatory mechanisms of certain organisms in order to make this material available to us," says Bill.
Tobacco "mosaic" viruses infect plants and manipulate their genes, causing leaves to take on a mosaic coloring. In the laboratory, however, this virus takes on the role of a catalyst. When the virus particles are placed in a supersaturated solution of zinc nitrate, the coveted zinc oxide precipitates and forms its regular structure. Depending on how the researchers change the composition of the viral proteins, the zinc oxide crystal will form into various structured layers. Some of them resemble a sponge while others look like a close-cropped lawn. "We can create specially structured layers with different material properties on a micro and nano scale," explains Bill.
Synthetic biology combines bimolecular processes with engineering concepts. In this field, as in biotechnology, biological cells function as miniature factories. Through special manipulation, scientists are able to form structures that do not exist in nature. Nediljko Budisa, head of the Research Group Molecular Biotechnology at the Max Planck Institute (MPI) for Biochemistry in Martinsried, calls it "code engineering." These scientists drive ordinary microorganisms to produce protein compounds that life has yet discovered. These artificial proteins may even help the plastics industry to develop more environmentally friendly and efficient materials in the future. Used in detergents, synthetic proteins would be ten times more effective than conventional anti-grease products.
Early on, scientists were just dabbling with these processes. In the 1960s, genetic researchers began to experiment with amino acids to find out how nature composes proteins and what could happen when these construction plans are amended. Proteins are the main players in the body: they transport materials, carry messages, and run vital processes as molecular machines. These "men of the control cell" are composed of amino acids whose sequences are determined by genetic information. Even the translation of this information during the formation of proteins is determined by the genetic code.
"All living things use a standard set of 20 different amino acids from which proteins are formed," says Lars Merkel, a member of Budisa's research team. But nature uses only a narrow repertoire of theoretically possible amino acids. "Many amino compounds are missing, such as the ones that contain the atoms fluorine, chlorine, bromine and silicon," explains Merkel. Living organisms have no use for these elements. However, these building blocks may be able to produce new therapeutic proteins and industrially important enzymes.
MPI researchers have gotten much closer to reaching their goal. In the laboratory, they have produced several new amino acids, including one that contains the element fluorine. But how can these artificial blocks be transferred to a target protein, in order to modify it for a specific application? Nature, uninterested in these materials, never developed a construction plan for the scientists to mimic. So they try something new: intestinal bacteria strains, which are not able to produce some of the 20 natural amino acids themselves.
These microbes must therefore acquire the missing amino acids from whatever growth medium they are in. When these acids are used up, the bacteria are faced with withdrawal, and will begin accepting similar structured compounds. The researchers begin to add small amounts of a fluorine-containing amino acid to the nutrient solution.
Some of the microbes are not particularly selective. They accept the artificial building blocks, build them into the target protein, and even begin to multiply. During this process, the synthetic amino acids transfer their properties to the proteins. Today, researchers are able to replace up to three amino acids with artificial compounds during a single experiment.
"This process might help us to develop entirely new classes of products whose biochemical syntheses we were previously unable to tap," says Merkel. Thus, with fluorine-containing proteins, catalysts can be created to work in both organic solvents and water. "It's like the Teflon pan, where a fluorine coating ensures that no water or fat can stick," he adds. Industry could use such catalysts well, as plastics containing fluorine must now be produced chemically through energy-consuming processes. Thanks to this new method, fluorine biomaterials could be produced cheaply and in an environmentally friendly manner. That's big work for such small organisms.
Read the original article in German