Biofertilizers and genetics

SIGNIFICANCE: Growth in the global population has resulted in the need for more food. Synthetic fertilizers and pesticides have increased crop yield. Resulting long-term harm to the environment, however, makes this approach unsustainable. As the world’s population grows to 9.8 billion by 2050 and 11.2 billion by 2100, genetic applications of ecofriendly biofertilizers offer promising results without devastating environmental damage.

Biofertilizers for Sustainable Agriculture

The increase in worldwide population has resulted in the global need for more food. The use of artificial fertilizers and synthetic pesticides has produced extensive short-term growth in crop yield and food production. However, the direct and indirect environmental impact of these chemicals include poor quality, mineral-depleted soil; toxic chemicals and metals in the soil; air pollution; poisoning of lakes and rivers through run-off and chemical leaching; premature births; and general disruption of the ecosystem. Despite the increase in food production, the environmental damage by commercial fertilizers makes this option unsustainable for future farming. As the world’s population increases, this challenge demands healthier alternatives to meet the agricultural needs of the world.

Just as the human genome has been sequenced for greater medical insight, scientists are using agricultural to capitalize on the genetic properties of both plants and microorganisms. Ecofriendly biofertilizers have been developed to augment or replace commercial synthetic fertilizers. They consist of natural living (“bio” means “life”) bacteria added to the soil, seed, or plant surface to enhance plant fertility. These beneficial microbes are often incorporated into various materials such as peat moss and applied to the plant’s soil to promote the health of the microflora and produce more and better crops. They enrich soil quality, prevent infections from phytopathogens, and lessen the stress of heavy metals left in soil by commercial fertilizers. Biofertilizers offer positive production outcomes without irreparable damage to the environment.

How Biofertilizers Work

Biofertilizers work in diverse ways to support plant growth. The goal is to provide a higher level of ecofriendly bacteria than are normally found in the soil so that plants can thrive when necessary nutrients are unavailable. Biofertilizers improve the growing environment of plants by adding organic material to enrich the physical condition and texture of the soil and minimize erosion. Some use the biological process to mobilize or “fix” the nutrients needed for plants to flourish. They can also have an impact on the microbial actions in the rhizosphere (around the roots) of the plant.

There are several types of biofertilizers available. Nitrogen-fixing biofertilizers contain bacteria that extract nitrogen (N₂) from the air and convert it to a form (N₃) that can be used by the plant. Common nitrogen fixers include Rhizobium, used primarily for legume inoculation where the bacteria invades the root, multiplies in the plant cortex cells, and produces nodules. This is a symbiotic relationship whereby the plant provides the Rhizobium bacteria with food and energy while the resulting nodules provide nitrogen fixing. Azotobacter microbes use nitrogen in cell protein synthesis that frees nitrogen for the soil at cell death. When Azotobacter bacteria are applied to seeds, they can improve germination and help control plant disease. Azospirillum bacteria and cyanobacteria (blue-green algae) are also nitrogen fixers. Xanthobacter autotrophicus has also been genetically engineered to produce ammonia (NH₃) from atmospheric nitrogen and hydrogen (H₂) for plants.

Phosphate solubilizers dissolve inorganic phosphorus from insoluble materials to assist with plant growth and produce increased crop yield. Examples of phosphate solubilizers include Pseudomonas, Xanthomonas, and Bacillus megaterium microbes. Mycorrhizae occur when Acaulospora, Endogone, Gigaspora, and Glomus fungi receive carbon from the plant and in turn provide nutrients for the plant, again increasing crop yield.

Additionally, some bacteria mediate the regulation of plant-growth hormones, such as auxins, gibbelleric acids, cytokinins, ethylene, nitric oxide, and polyamines.

Further research is required to understand and modify the complex interactions between various microbes and crop plants in the field. One challenge for agricultural biotechnology is that subsequent rounds of biofertilizer application have proved less effective than the initial treatment, with inefficient bacteria proliferating and requiring additional nitrogen-based fertilizers. The emerging study of multiple organisms' genomes within a community is known as "metagenomics."

Benefits of Biofertilizers

Biofertilizers offer many benefits in agricultural biotechnology. First, they are cost-effective as compared with petroleum-based fertilizers. While synthetic fertilizers require repeated use of large quantities and produce the adverse effect of depleting the soil of nutrients, biofertilizers enrich the soil with naturally occurring microbes and stay in the soil for a longer time. A major benefit is accelerated plant growth with an increase in crop yield, as high as 60 percent in certain crop plants. Plants supported with biofertilizers demonstrate greater pest and disease resistance, requiring less costly applications of pesticides. The soil itself shows better water-holding capacity and growing space while minimizing detrimental changes in pH levels. A major benefit of biofertilizers is that they are naturally occurring and contain no substances that can harm food and water.

Impact

In this world of limited resources and growing population demands, scientists are looking for ways to use genome biology and analysis to improve various aspects of human life. Between 1994 and 2005, Microbial Genomics, a branch of the US Department of Energy (DOE) Office of Science, sought to define new ways to use microbes to uncover alternative energy sources, to define the process of biological carbon cycling, and to clean up toxic environmental wastes. By March 2014, this group, along with the DOE's Genomic Science Program, had completed genomic sequencing of more than 541 microbes. As of July 2018, the DOE Joint Genome Institute's Integrated Microbial Genomes database cataloged nearly 78,000 genomes of archaea, bacteria, and eukarya. DOE scientists believe that microbes offer untold benefits for applications to the environment, health, industry, and energy. One specific application of microbes is in the development and use of biofertilizers.

Biofertilizers employ microbes to achieve greater positive, ecofriendly results when compared with costly petroleum-based fertilizers. With demands to “go green” and minimize adverse environmental damage, agricultural biotechnology provides reasonable, cost-effective alternatives for crop yield maximization. Applying genome principles and study to biofertilizers looks promising for the future of food production for countries around the world. During the mid 2020s, the biofertilizer market slowed considerably, as farmers turned away from the product due to poor shelf life and special handling requirements.

Key Terms

• agricultural biotechnologytechnology that employs scientific tools to modify the genetics of an organism for a practical agricultural purpose
• biofertilizersfertilizers that contain living organisms (bacteria or fungi) used to enhance availability and uptake of minerals in plants and improve fertility
• microbial inoculantsmicrobes introduced into the soil or plant to build symbiotic relationships for mutual benefit between microbes and plants; used in organic farming
• mycorrhizaesymbiosis that occurs between fungi and plants; fungi colonize the cortical tissue of roots in active plant growth and receive carbon from the plant while providing the plant with needed nutrients for growth
• nitrogen fixersbiofertilizers that use microbes to take nitrogen from the atmosphere and turn it into usable material to promote plant growth
• phosphate solubilizerbiofertilizers that use microbes to dissolve inorganic phosphorus from insoluble materials to produce increased crop yield
• symbiosisa living together, close union, or cooperative relationship of dissimilar organisms to create a state of mutualism, where each party benefits from the relationship

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