Marine Bacteria Offers Eco-Friendly Nitrogen Source

According to recent research published in npj Sustainable Agriculture, Rhodovulum sulfidophilum, a purple photosynthetic marine bacterium, can be used to make biomass, which is a highly effective nitrogen fertilizer. The research led by Keiji Numata of Kyoto University and the RIKEN Center for Sustainable Resource Science (CSRS) demonstrates that this biomass is as effective as popular inorganic synthetic fertilizers without many negative environmental side effects.

With rising global food demands, increasing agricultural output through the use of nitrogen-rich fertilizers is a common practice that is anticipated to intensify in the upcoming decades. Excessive use of common inorganic nitrogen fertilizers is also anticipated to have a severe negative impact on the environment, leading to significant greenhouse gas emissions, contaminated ground water, and poor soil quality.

However, because fertilizers contain a lot less nitrogen, organic fertilizers like compost and manure need to be applied in larger quantities to have the same impact on plant growth. In the long run, this results in more carbon dioxide and nitrous oxide byproducts as well as toxic, plant-growth-stunting, excessively salted soil.

To avert a potential crisis, the Biomacromolecules Research Team at RIKEN CSRS has been looking for a natural source of nitrogen to replace synthetic fertilizers based on ammonia. Although it is known that purple non-sulfur bacteria (PNSBs) possess enzymes that enable them to absorb nitrogen from the atmosphere and incorporate it into proteins, their efficacy as fertilizers has not yet been investigated.

The researchers mashed up the PNSB R. sulfidophilum and produced dried biomass from the released cellular material to make a PNSB fertilizer for the new study. According to analysis, the PNSB fertilizer had 11% by weight of nitrogen, which is significantly more than other organic fertilizers that contain biomass derived from other microbes or microalgae.

The growth rates of the Japanese mustard spinach komatsuna (Brassica rapa var. perviridis) with and without the new PNSB biomass fertilizer were compared by the researchers. The first significant discovery was that mustard spinach could absorb nitrogen from the dried biomass.

Subsequent tests revealed that in both cool and warm temperatures, the biomass fertilizer increased plant growth in the same way as the nitrogen-rich inorganic fertilizers. Furthermore, soil pH and salinity remained normal, comparable to soil fertilized without any nitrogen, even when the biomass fertilizer contained up to four times the amount of nitrogen.

In comparison to inorganic fertilizers, the PNSB biomass fertilizer has a low carbon-to-nitrogen ratio and releases nitrogen for plant uptake relatively slowly—roughly 60% in 30 days.

The big benefit is that there will be fewer emissions of carbon dioxide and nitrous oxide and less nitrogen leaching into the environment, even though this means twice as much biomass fertilizer will be needed for similar crop growth.

In the long term this could revolutionize agriculture and mitigate its negative impact on the environment.”

Morey-Yagi, Study Lead Author, RIKEN

The basic experiments demonstrate the biomass fertilizer’s effectiveness, but the authors emphasize that these are preliminary results and that additional factors will eventually need to be taken into account.

Numata explained, “A life-cycle assessment of this fertilizer will be essential for evaluating its environmental footprint across production, storage, application, transport, and disposal.” Additionally, how to scale-up the biomass production process must be considered, and shelf-life must also be established.

The researchers hope to overcome these obstacles, that their findings will contribute to the development of more environmentally friendly fertilizers, and that they will help avert future issues with the inorganic fertilizer supply chain.

The researchers have registered the biomass fertilizer as Air Fertilizer^® and registered it as an organic fertilizer in Japan under the Symbiobe Inc. brand. This is because the fertilizer is made using carbon dioxide and nitrogen from the air.