Legions of armored bacteria: it might sound ridiculous, but this is actually a real agricultural innovation that now provides a promising alternative to conventional fertilizer across the world’s farms, according to new research.
In a recent study, a team of scientists have found a way to seal nitrogen-fixing bacteria with a protective coating so that they survive desiccation and high temperatures. This enabled the bacteria to fertilize and improve the germination rates of corn and bok choy by 150%.
Such bacteria, like Pseudomonas Chlororaphis which fix soil nitrates into usable nitrogen for plants, are a promising alternative that many farmers already use. Natural, regenerative methods of nourishing plants like this are seen as a way out of the emissions-intensive bind of conventional fertilizers, whose production contributes 1.5% of global greenhouse gas emissions each year—and that’s before they even strike the soil.
But the extreme temperature- and moisture-sensitivity of nitrogen-fixing microbes has made it difficult to transport them long distances, typically limiting their applications to those farms where bacteria can be expensively cultivated in bioreactors, on site. Seeing its huge potential, the researchers were determined to “democratize” this sustainable fertilizer alternative, making it accessible across global farmland.
Their starting point was a technology they had already tested to protect therapeutic drugs on their passage into the human body, called metal-phenolic networks (MPNs). These are mesh-like structures made from thin layers of metal, combined with polyphenols, which are naturally-occurring compounds such as antioxidants. Crucially, these networks self-assemble, and can form several layers around microscopic objects like a bacterial cell.
For their study, the researchers created 12 different metal-phenol combinations, which they applied in either two or four layers to P. Chlororaphis. Then they exposed the newly-armored microbes to freeze-drying, high temperatures of 50°C, and intense humidity. At the end of the experiment they grew seeds including corn, bok choy, sprouts, radishes, and dill in a mixture containing the special bacteria, to see how it affected their growth.
Without a doubt, the MPN coverings conveyed incredible powers of resilience to the sensitive microbes, the experiments proved. Within all 12 combinations, the bacteria fared better than those that went without the protective casing and swiftly perished under the temperature and moisture extremes. The best-performing MPNs enabled some extraordinary feats of survival: under 50°C and intense humidity, the enclosed bacteria survived for 10 days. Incredibly, under 30°C conditions, they could last for two months.
What’s more, when these more resilient bacteria were applied to the growing medium of seeds, they increased the germination rate of those plants by 150% compared to even uncoated bacteria that had been freshly applied to the soil. It’s unknown why the coated bacteria had an advantage over the fresher microbes in this case; that’s a question researchers hope to dig into more.
In the meantime, the fact that the bacteria can last for such impressive periods of time under hot conditions and desiccation “pushes the protective ability of our coatings into the realm of utility for regenerative agriculture,” the researchers write. In other words, the benefits of these natural fertilizers are no longer dependent on expensive bioreactors or cold-chain storage; instead they could be made into practical forms like dried powders that can be easily transported to farms far and wide, and mixed into the soil.
Getting closer to that reality will require a huge scale up of the researchers’ invention, hopefully helped by their recent venture to commercialize the coated bacteria. The cheap production process should make it accessible to most farmers around the world, they say. Long-term, they believe these microscopic power houses could even “be viable, sustainable alternatives to chemically-produced fertilizer.”
First et. al. “Self-Assembled Nanocoatings Protect Microbial Fertilizers for Climate-Resilient Agriculture.” JACS Au. 2023.
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