Researchers have demonstrated a technique for successfully encapsulating bacteria that can then be stored and applied to plants to improve plant growth and protect against pests and pathogens. The technique opens the door to creating a wide range of crop applications that allow farmers to make use of these beneficial bacteria in conjunction with agrochemicals. The paper, “Pickering Emulsion for Enhanced Viability of Plant Growth Promoting Bacteria and Combined Delivery of Agrochemicals and Biologics,” is published in the journal Advanced Functional Materials.
“Many of the beneficial bacteria we know of are fairly fragile, making it difficult to incorporate them into practical, shelf-stable products that can be applied to plant roots or leaves,” says John Cheadle, co-lead author of a paper on the work and a Ph.D. student at North Carolina State University. “The technique we demonstrate here essentially stabilizes these bacteria, making it possible to develop customized probiotics for plants.”
At issue are plant growth-promoting bacteria (PGPBs), which are microbes that benefit plant health and growth, helping plants extract nutrients from the environment and protecting them from pests or pathogens.
“A longstanding challenge for making use of these bacteria has been that if you tried to come up with a single application that combined them with agrochemicals, like pesticides or fertilizers, the bacteria would die,” says Saad Khan, co-corresponding author of the paper and INVISTA Professor of Chemical and Biomolecular Engineering at NC State. “We wanted to develop a solution that would allow bacteria to be used in conjunction with chemicals already in widespread use by growers.”
“By the same token, a healthy plant microbiome allows the plants to make better use of nutrients available in the soil and more resistant to pathogens,” says Tahira Pirzada, co-corresponding author and a research scholar at NC State. “This may allow growers to use less fertilizer and pesticides without hurting crop production.”
The new technique revolves around a custom-made emulsion, with only a handful of ingredients. One part of the emulsion consists of a saline solution that contains PGPBs. For the proof-of-concept demonstration, the researchers used the bacteria Pseudomonas simiae and Azospirillum brasilense. P. simiae acts as a biopesticide by promoting pathogen resistance; A. brasilense acts as a biofertilizer by fixing nitrogen.
The second part of the emulsion consists of a biodegradable oil and a biodegradable polymer derived from cellulose. The polymer can be loaded with agrochemical active ingredients, which means the emulsion can incorporate these ingredients without relying on environmentally harmful organic solvents, which are typically used in pesticide formulations.
When the two parts of the emulsion are mixed together, the oil is broken into droplets that are distributed throughout the saline solution. The cellulose polymer sticks to the surface of these droplets, preventing the droplets from merging back together.
Essentially, the emulsion is a salad dressing with the oil droplets held in suspension throughout the saline solution. In practical terms, this would allow the PGPBs to be applied simultaneously with agrochemicals using the same emulsion.
To see how well the emulsion worked, the researchers did two tests.
First, the researchers compared the survival of PGPBs in the emulsion to the survival of PGPBs in the saline solution alone. Samples of each were stored at room temperature. After four weeks, the population of P. simiae in the emulsion was 200% higher than the population in saline; the population of A. brasilense in the emulsion was 500% higher.