Biogenic selenium nanoparticles from marine Pseudoalteromonas shioyasakiensis VB17: Physicochemical characterization and preliminary stimulation of seed germination
Marine bacterium *Pseudoalteromonas shioyasakiensis* VB17 was utilized to synthesize stable, protein- and polysaccharide-coated biogenic selenium nanoparticles that exhibit no toxicity toward specific microbes and effectively enhance seed germination and early seedling growth in wheat and buckwheat.
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Selenium is a trace element that plays a vital role in the health of humans and animals, acting as a shield against cellular damage and helping to regulate hormones. While plants do not strictly need it to survive, small amounts can act like a vitamin for them, helping crops grow stronger and better withstand harsh conditions like drought or salty soil. However, selenium is a double-edged sword. In its common chemical forms found in nature, it can be toxic to plants if the dose is too high, causing stress that stunts growth or kills the seedling. Scientists have long searched for a way to deliver this element to plants safely, aiming for a form that the plant can absorb easily without suffering from toxicity. One promising solution involves turning selenium into tiny particles, so small that they are measured in billionths of a meter. These nanoparticles can interact with plant biology in unique ways, potentially offering the benefits of the element while avoiding the dangers of its raw chemical forms.
To create these particles, researchers often look to nature itself rather than industrial factories. Instead of using harsh chemicals or high energy to manufacture nanoparticles, scientists can harness the natural abilities of microorganisms. Certain bacteria act as tiny factories, taking dissolved selenium from their environment and transforming it into solid, harmless particles. This process, known as biogenic synthesis, is considered a greener and more sustainable way to produce these materials. The specific bacteria used can influence the size, shape, and surface properties of the resulting particles, which in turn determines how well they work when applied to crops. The challenge lies in finding the right bacterial strain and the perfect conditions to produce particles that are both effective and safe.
In a recent study, researchers turned their attention to a specific marine bacterium called Pseudoalteromonas shioyasakiensis VB17, which was originally isolated from the waters of Nha Trang Bay in Vietnam. The team wanted to see if this ocean-dwelling microbe could efficiently convert toxic selenium into useful nanoparticles and, if so, whether those particles could help plants grow. They began by testing how the bacteria behaved under different conditions. They mixed the bacteria with varying amounts of selenium and adjusted the number of bacterial cells in the mixture to find the sweet spot for production. They discovered that having more bacteria initially helped speed up the process of turning the toxic selenium into solid particles, but only up to a point. If the selenium concentration was too high, having too many bacteria actually slowed things down and reduced the total amount of selenium converted. The researchers identified a specific balance: a moderate number of bacteria mixed with a specific, moderate amount of selenium worked best. Under these conditions, the bacteria rapidly transformed the selenium, creating a stable suspension of nanoparticles.
Once the nanoparticles were produced, the researchers examined them closely to understand what they were made of and how they looked. Using powerful microscopes and light-based analysis tools, they found that the particles were mostly round or slightly oval in shape. The individual particles ranged in size from about 80 to 135 nanometers, which is incredibly small, yet they were large enough to be seen with advanced imaging equipment. Inside these particles, the selenium formed a crystalline structure, meaning the atoms were arranged in a neat, repeating pattern, which is a sign of a stable and well-formed material. The analysis also revealed that the surface of these particles was coated with natural biological molecules, specifically proteins and sugars, which the bacteria released during the process. These coatings act like a protective shell, keeping the particles stable in water and preventing them from clumping together immediately. The particles also carried a strong negative electrical charge, which helps them repel each other and stay suspended in liquid, a crucial feature for applying them to plants.
The next step was to see if these biologically made particles were safe and effective. The researchers first tested them against common soil bacteria and fungi to ensure they would not harm beneficial microorganisms. At the concentration they tested, the nanoparticles showed no signs of killing or stopping the growth of these microbes, suggesting they are compatible with the soil environment. They then moved on to test the particles on seeds. They treated seeds of wheat and buckwheat with a solution containing the nanoparticles and watched how they grew compared to untreated seeds. The results were encouraging. The treated wheat seeds sprouted more reliably and grew into stronger seedlings. The young wheat plants developed longer roots and shoots, and their overall weight increased significantly compared to the control group. The buckwheat seeds also showed a marked improvement in germination rates, with far more seeds sprouting successfully.
These findings suggest that the marine bacterium VB17 is a capable producer of selenium nanoparticles that are both safe for beneficial microbes and beneficial for plant growth. The study provides a clear example of how a specific strain of bacteria can be tuned to produce particles with specific characteristics, such as size and surface coating, which are essential for agricultural use. While the results are promising, the researchers note that this is an early stage of investigation. The experiments were conducted in a controlled laboratory setting, and only one specific concentration of the nanoparticles was tested. Future work will need to determine the best dosage for different crops and verify that these benefits hold true in real-world fields and greenhouses. Nevertheless, this study offers a compelling glimpse into a future where ocean bacteria could help solve land-based agricultural challenges, turning a potentially toxic element into a tool for healthier, more resilient crops.
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