Wearing silk may help seeds grow

A protective silk coating that supplies essential nutrients may make it possible to grow seeds in soil that is otherwise seen as unproductive. 

Engineers from Massachusetts Institute of Technology in the US coated the seeds with silk treated with rhizobacteria, a bacteria that produces a nitrogen fertiliser.

While rhizobacteria occurs naturally in soils around the world, with different varieties found in different regions, it’s difficult to preserve outside its natural soil environment.

That’s where the silk comes in. 

It can preserve biological material, says co-author Benedetto Marelli, and it is also water-soluble “so as soon as it’s exposed to the soil, the bacteria are released”. 

Marelli and colleagues found that the coating was strong enough to protect the seeds, while the nutrients allowed the seeds to germinate in soil with a salinity level that would ordinarily prevent their normal growth.

“We do see plants that grow in soil where otherwise nothing grows,” he says.

It wasn’t all smooth sailing, however. In preliminary tests, the team found that the bacteria they added to the silk coating wasn’t as well preserved as expected.

To fix this, they added a kind of sugar known as trehalose into the mix. The sugar is used by some organisms to survive under low-water conditions. 

The researchers then suspended the silk, bacteria, and trehalose in water before simply soaking the seeds in the solution for a few seconds.  

The resulting plants, helped by ongoing fertiliser production by the bacteria, were healthier than those from untreated seeds. They also grew in soil from fields that are presently not productive for agriculture, the researchers report in the journal Proceedings of the National Academy of Sciences.

The researchers hope this process, which can be applied inexpensively and without the need for specialised equipment, could create new areas of farming land that were previously thought to be unsuitable for agriculture.

Co-author Augustine Zvinavashe says the process of dip-coating the seeds can take a few seconds, meaning it is quick and easy and “might be scalable”.

The first tests were undertaken indoors, under controlled conditions. Next year the researchers plan to begin outside plantings in experimental fields.

They also are working on a new coating that would also make the seeds more resistant to drought by absorbing the water from the soil.