In 2024, food security is a pressing global issue; even with sufficient global food production, in some parts of the world the problem is worsening. For example, in some areas of Africa, food security is dire. Food security is a complex issue that is used to describe those without access to any food or those with access to limited food types, therefore resulting in malnutrition

The United Nations (UN) strives to end hunger, food insecurity, and malnutrition in all forms. This is part of their 2030 Agenda for Sustainable Development, which involved the creation of the Sustainable Development Goals (SDGs).

The Sustainable Development Goals (SDGs) are 17 goals which provide a shared blueprint for peace and prosperity for people and the planet now and into the future. Goal 2 is to end hunger, achieve food security and improved nutrition and promote sustainable agriculture. In order to make this goal achievable, the UN has created individual targets to reach, such as target 2.1:

“by 2030, end hunger and ensure access by all people, in particular the poor and people in vulnerable situations, including infants, to safe, nutritious and sufficient food all year round”.

The SDGs have inspired various scientists’ and activists’ projects to address the goals and advance sustainability. Here, we look at research recently published in the Open Access journal Plants that analyses the freshwater fern species Azolla, a potential solution to global food security for toxicity.

“I felt a sense of responsibility to help answer this question because we had just published about Azolla’s nutritional quality. I didn’t want to be promoting the consumption of a potentially harmful plant. As I was preparing an experimental design, I was contacted by the Azolla Foundation about that organization’s interest in our research. I reached out to them and asked if they knew anyone who was looking into Azolla’s toxicity from cyanotoxins.” – Dr Daniel Winstead, author on the paper.

What is Azolla?

Azolla Lam., also referred to as Azolla, is a floating freshwater fern that has been cultivated for centuries, mostly across Asia. It has a symbiotic relationship with the cyanobacteria Nostoc azollae (N. azollae), and because of this, it can rapidly fix nitrogen.

This process converts nitrogen from the atmosphere into compounds like ammonia or nitrate, which support plant growth. This allows Azolla to grow and reproduce quickly; additionally, it can grow in nutrient-deficient environments. It can double its biomass in two days while floating on fresh water without any fertilizers.

Moreover, it has also been used in India for generations as a biofertilizer, increasing the yield of paddy rice. It is even a natural repellent of mosquitoes as it covers the water surface. This prevents mosquitoes from laying eggs and breeding in paddy rice fields.

Azolla and food security

“Azolla is an amazing plant that can double its biomass in two days and capture nitrogen from the air.” – Professor Francesco Di Gioia, author on paper.

Azolla has also been utilised in paddies, which are flooded fields used to propagate the growth of rice. Paddies naturally produce the potent greenhouse gas methane. Because of this, they can be enhanced via dual cropping with Azolla, which has been shown to reduce emissions.

The list of uses for Azolla continues to grow as researchers investigate their properties. This includes food for livestock, providing positive effects on their nutrition; biofuel and biofertilizer for other plants; and absorbing nitrates and phosphates from water contaminated by pollutants. These pollutants include chemical fertilisers and animal and human waste that can trigger blooms of toxic cyanobacteria in lakes and rivers.

Azolla has the potential to be used to meet the demand for food security globally due to its ability to reproduce rapidly. Additionally, it is an ideal crop to propagate as it can be grown in a variety of environments, including tropical and temperate regions.

Testing for cyanotoxicity

Penn State researchers previously investigated ways to use Azolla to help meet food security demands. However, this research raised concerns regarding how Azolla’s association with cyanobacteria, N.azollae, may prevent it from being safe for humans to consume.

N.azollae is a cyanobacteria which  lives on the Azolla plant. Cyanobacteria often harbour harmful cyanotoxins, which are some of the most powerful natural poisons. They are neurotoxins that target the nervous system and have been linked to the development of neurodegenerative diseases such as Alzheimer’s and Parkinson’s. Neurotoxins target the nervous system and have been linked to the development of neurodegenerative diseases such as Alzheimer’s and Parkinson’s. In addition, they have been linked to other health conditions such as liver and kidney failure, muscle paralysis, and other severe health issues.

Because of this, a researcher from the Penn State study collaborated with other researchers from a variety of locations, including the UK, Portugal, Vietnam, and Switzerland, to investigate the potential toxicity of 48 variations of the Azolla–Nostoc symbiosis.

Results of toxicity analysis

The researchers analysed 7 species of Azolla for the presence of genes that synthesise cyanotoxins. The 7 species of Azolla tested include A. caroliniana, A. filiculoides, A. mexicana, A. microphylla, A. nilotica, A. rubra, and A. pinnata. In addition, the researchers also tested subspecies A. pinnata subsp. pinnata and A. pinnata subsp. Imbricata.

“Together, we analyzed the results and concluded that Azolla, and more specifically a cyanobacterium that lives in cavities in the leaves of Azolla, do not produce any of the main cyanotoxins,” he said, explaining that Azolla’s cyanobacterium is Nostoc azollae, an endosymbiont or organism that lives within or on the surface of another organism in a mutually beneficial relationship. “More importantly, the known genes required to make these toxins are not even present within the genome of Nostoc azollae.” – Dr Daniel Winstead.

The analysis included 48 accensions of the Azolla species and isolated N. azollae cyanobacteria symbionts. The DNA from isolated N. azollae and the Azolla accessions were extracted and amplified using a polymerase chain reaction (PCR) to analyse 12 genes that encode for 4 cyanotoxins: cylindrospermopsin, nodularin, saxitoxin, and microcystin.

The N. azollae was then analysed using nucleotide BLAST to identify the genetic sequences associated with the production of the neurotoxin, anatoxin-a. BLAST analysis is a bioinformatics tool used to identify regions of similarity between genetic sequences of interest and those in a database.

Finally, the 7 species and 2 subspecies of Azolla were analysed using liquid chromatography mass spectrometry (LC/MS/MS) to determine the presence of neurotoxin β-N-methylamino-L-alanine (BMAA).

Toxicity of Azolla species

The researchers identified that Azolla and N. azollae species do not have the genes to produce cyanotoxins: saxitoxin, cylindrospermospin, microcystin and nodularin. Furthermore, the BLAST analysis did not indicate the presence of the anatoxin-a gene in the N. azollae genus. The LC-MS/MS analysis also showed that BBMA and its isomers AEG (N-(2-aminoethyl)-glycine) and DAB (2,4-diaminobutyric) are absent from Azolla and N. azollae.

“That finding suggests that azolla is food safe and has the potential to safely feed millions of people due to its rapid growth while free-floating on shallow fresh water without the need for nitrogen fertilizers.” – Dr Daniel Winstead

Because of this, the researchers concluded that Azolla is safe for humans to consume and could help to provide millions with food sources, helping to improve food security for all.

“It could help feed many people in need around the world as well as become a new source of biofertilizer and biodiesel.”- Dr Daniel Winstead

If you’re interested in reading more on this subject or would like to submit research, please see our recent topic Plant Ecology for more information.