The home dialysis machines of kidney patients will contain Dutch jack beans

It all started 14 years ago with an initiative by the Dutch Kidney Foundation and three health insurers. Together, they worked on a home dialysis device: the Neokidney. Harmen de Jongh of Nextkidney, the company developing the Neokidney, explains why the device is so valuable. “Normally, a patient goes to a clinic every three days for dialysis. That is because of the large volume of fluid needed for dialysis – around 150 litres. The Neokidney is a compact dialysis device weighing 10 kg that you can easily take with you. It contains a filter that cleans the dialysis fluid so it can be reused. As a result, you only need 4 to 5 litres of fluid.”

An essential part of this filter is the enzyme urease, De Jongh continues. “In its active form, this enzyme breaks down the waste product urea. Compared with other crops, jack beans contain relatively high levels of active urease. That makes them a very suitable source. Urease can also be produced in a bioreactor, but once you isolate it, it quickly loses its activity.”

The problem with jack beans, however, is that the right type of bean is mainly grown in China, says De Jongh. “There, they are cultivated on a very small scale, often as a soil improver. Commercially, it is not an attractive crop. For the production of filters, we entered into a partnership with a farmers’ co-operative in China. We import around 20 tonnes of beans from them each year. But given the geopolitical tensions, uncertainty about continuity of supply and the environmental impact of transport, we cannot be too dependent on imports from abroad.”

That is why, in 2022, De Jongh approached Dolf Straathof and Jeroen Zonneveld of Unifarm, WUR’s plant research facility, to ask whether the bean could also be grown in the Netherlands. Straathof explains: “From his time at WUR, Harmen knew that we had the necessary resources and expertise here. Because so little was known about cultivation, we had to start almost from scratch. The first thing we wanted to know was how the plant should be pollinated and whether it would also grow under 16 hours of light a day. Because the jack bean is originally a tropical crop, we were concerned that it might be a short-day plant. If it gets more than 12 hours of light, there is a chance it will not produce beans.”

In a trial set-up in the Unifarm greenhouses, the researchers grew the beans under both short-day and long-day conditions. There was a sigh of relief when plants with pods appeared under both conditions, says Straathof. “What is more, all the plants shot up in no time, some of them right up to the roof. Just like in Jack and the Beanstalk, to which the bean owes its name. Thanks in part to urease, the plants convert nitrogen very rapidly. The fact that the plant also grows under long-day conditions was an important first step. It means we do not need expensive interventions and installations to darken the greenhouses.”

Once the pods had ripened and been shelled, the researchers were pleased to find a batch of well-formed beans. But the mood changed when De Jongh returned with the analysis results. The beans did contain urease, but not in its active form. De Jongh says: “That meant we could not use them in the filter. I strongly suspected that the explanation lay in the composition of the soil. We then took soil samples from farmers in southern China. Thanks to Zonneveld’s contacts at a local research lab, those samples could quickly be analysed for their mineral composition.”

According to Straathof, the lab results were startling. “It looked as if the beans were growing on a scrapyard. The soil naturally contained high levels of heavy metals, such as iron and nickel. Nickel is an important activator of enzyme activity. Back in Wageningen, we started testing different concentrations of soluble iron and nickel in the substrate. In the pots with iron, the plants barely grew, but in those with nickel, they did. At the selected dosage, the level of active urease in the bean was almost twice as high as in beans from China. That was our eureka moment.”

With this, the researchers had shown that jack beans can also be grown successfully in the Netherlands. To make the move from research to practice, De Jongh began looking for growers willing to cultivate the bean. He found them in the West Brabant and Westland regions, where, since 2024, seven greenhouse growers within a consortium have been growing jack beans in part of their greenhouses.

Straathof says: “The great thing is that each grower uses a different cultivation method. They use different substrates, irrigation and fertilisation methods, and different planting densities. That gives us insight into what delivers the best results. At the moment, cultivation is still very limited. Altogether, it is not yet even a full hectare. With 1 hectare, you can provide around 200 patients with filters for home dialysis for a year. To supply enough dialysis filters for all kidney patients in the Netherlands, we will eventually need 40 to 50 hectares. For greenhouse production, that is a considerable area.”

Meanwhile, work in Wageningen is continuing, Straathof emphasises. “There is still a great deal to find out. Thanks in part to a grant from Regiodeal Foodvalley, we were able last year to continue experimenting with other crops, such as soy. That bean also contains urease, but in much lower concentrations and with less activity. We are also looking at the possibilities for outdoor cultivation. That could be interesting for countries in southern Europe. We are also investigating whether nickel can be applied through the leaves, and we are testing different nickel concentrations to find out whether there is an optimum.”

At the same time, the researchers are also examining potential risk factors, such as safety and environmental impact. Straathof says: “Nickel is a heavy metal, so it has to be applied very responsibly, and the soil containing nickel must be handled with great care. The latter is particularly challenging in open-field cultivation. We still need to gather a great deal of information so that we can ultimately develop a robust and environmentally friendly cultivation system.”

De Jongh is extremely grateful to WUR for the collaboration. “What we have achieved over the past few years would normally take decades of research. What I find most rewarding is the enormous impact we can make with this. I have seen up close what a difference a home dialysis device can make. A kidney patient taking part in a trial told me that, thanks to the device, he was able to go away for a weekend with his wife for the first time in years. That really moves me and makes me very proud. We hope to bring the Neokidney to market next year. That would be a tremendous step forward. Not only for kidney patients, but also for growers, because it would make scaling up jack bean cultivation commercially attractive for them.”