Nitrogen is rarely thought of as a vital element, but it is still essential for life. While not as obvious as water, oxygen or carbon, it is nonetheless needed to synthesize DNA, RNA and amino acids for proteins, the basic building blocks of plants, animals and other life forms.
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Nitrogen fixation, the process by which atmospheric nitrogen is converted into the ammonia that is used as a nitrogen source, is complicated. Few bacteria can convert nitrogen from the air, but biological nitrogen fixation through plant-bacterium symbiosis is effective. Yet science still has much to learn about the process, and a pioneering European Union (EU)-funded research project is aiming to unravel the secrets of how plants interact with their bacterium partners, and how to help them perform better.
The project, called Sym-Biotics, is led by Hungarian biologist Éva Kondorosi, who is looking at the symbiotic relationship between legume plants and the nitrogen fixing soil bacteria known as Rhizobia. She believes that a better understanding of how symbiotic cells work can help us boost nitrogen fixation. That, in turn, could raise plant biomass production and deal with issues like food shortages and climate change. It could also mean applications such as novel antibiotics, green chemicals for plant protection, or agents against microbes such as listeria and salmonella.
"This is pure science, which could lead to numerous discoveries with potential benefits for humanity," says Kondorosi, who was the founder and director of the Institute for Plant Genomics, Human Biotechnology and Bioenergy (BAYGEN), part of the Biological Research Centre in Hungary's southern city of Szeged. "Our studies relate to the main challenges of the 21st century, namely to the need for higher agricultural production, enhanced food safety and protection against the alarming rise of antibiotic resistant pathogenic bacteria and fungi."
Sym-Biotics will run for five years until July 2016. Kondorosi, who was awarded a €2.32 million grant from the European Research Council (ERC), says the nitrogen fixing symbiosis is especially efficient in protein-rich food and feed legumes like alfalfa (a type of pea plant) and pea, whose root nodules host the bacteria and provide a treasure trove of antimicrobial activities. The bacterium-infected plant cells produce hundreds of peptides, the vital links that bond amino acids. "In a broader sense, the antimicrobial action of peptides can open many avenues of biotech applications," says Kondorosi.
One of the most intriguing possibilities is in medicine. With antibiotic resistant bacterial strains representing an increasing global health problem, peptides from edible plants could offer a solution as drug candidates against previously untreatable infections. "There is an urgent need for the development of new antibiotics with novel mechanisms," Kondorosi says. "We want to learn what the symbiotic peptides do with their bacterial partners, in order to use them as novel types of antibiotics." She has already identified a few peptides that act rapidly to kill a broad range of bacteria and fungi without toxicity to human cells.
Kondorosi says the Rhizobium-legume symbiosis could be a paradigm of other host-bacterium interactions, like insect-bacterium symbiosis where antimicrobial peptides also appear to control the maintenance of intracellular bacteria.
Moreover, stimulating nitrogen fixation could improve the fertility of the soil while sparing crops from exposure to harmful fertilizers, herbicides and pesticides. "I am convinced that there will be European benefits from the project," Kondorosi says. "We shall know more about symbiosis, how the plant controls the number and physiology of its bacterial partner and whether and how this results in more efficient nitrogen fixation."