Feijoa Research at Victoria University

November 2016

Searching for a novel anti-fungal agent produced by feijoas at Victoria University

Chemo-prospecting scientists could hold the key for elevating exports and adding value and utility for crops such as the feijoa. Researchers at Victoria University have combined forces with a passionate feijoa grower to search for unique metabolites within this humble little fruit. It’s hoped that the identification of unique chemical compounds will add value to different cultivars and aid selective breeding of desirable traits while developing an export market on par with horticultural heroes like the kiwifruit.

Nigel Ritson, a Takaka based feijoa breeder, approached Victoria University scientist Dr Rob Keyzers in 2013. Nigel is a passionate feijoa grower and breeder and had been closely observing and breeding his own unique cultivars. He had noted that when he cut a feijoa on the tree, it did not get infected with fungi and he knew something potent was at work. He was keen to better understand the properties of his different cross bred cultivars.

In broad terms the goal is to get feijoa moving in the direction of being a major food export for NZ, similar to kiwifruit.

Further aims include seeing if they have added value ‘clean & green’ bioactives (like an anti-fungal) that could be extracted from either the fruit pulp or waste residue (peel), and secondly to better understand his cultivars to continue his breeding programme. Thirdly identifying unique compounds within some of his cultivars that bear bad tasting fruit would give those a value fullstop.

In terms of selective breeding, the holy grail for any feijoa grower would be achieving a tasty and long life fruit. Presently feijoa have a short shelf life and do not travel well.

Rob Keyzers in the School of Chemical and Physical Sciences conducts research that involves the study of metabolites from food and wine to isolate and characterise novel bioactive compounds from New Zealand and the Pacific region. This bio-prospecting aims to find new pharmaceutical compounds for medical and added value applications. Bioactive natural products are a significant source of lead compounds for the development of clinically useful pharmaceuticals.

Rob quickly identified that there was “a nice link between chemical profiling and biological profiling” and teamed up with colleague Dr Andrew Munkacsi in the School of Biological Sciences.

Andrew’s research interests are at the “interface of genomics, medicine, and biodiversity”. In this feijoa project, genes and pathways underlying the bioactivity of the feijoa compounds are identified via analyses of every gene in the yeast genome (i.e the yeast being a fungi). With these results, the potential biomedical utility of the compounds can be predicted since yeast is an established model organism to study human biology. For example, his lab used yeast to identify the potential of treating a fatal, paediatric neurodegenerative disease with a particular drug (an HDAC inhibitor) and that drug is now being tested in human patients in a clinical trial in the USA.

The combined chemical and biological profiling approach uses many standard techniques in food science research labs. What is unique here is the biological resource in Nigel’s unique feijoa varieties, and in the unbiased statistical approach used to link the disparate observed biological activities and chemical profiles.

The feijoa project commenced with the testing of 16 cultivars supplied by Nigel (3 commercial cultivars and 13 unique to Nigel). Pulp and skin was taken from each cultivar, resulting in 32 samples. Each sample is then further refined, with chemicals extracted using solvents and prepped for testing.

Rob has utilised gas chromatography to profile the chemical compounds found in the cultivars. “Our premise is that chemical novelty equates to bioactive novelty as irrelevant metabolites are bred out through natural selection.”

Chemical profiling is used because all feijoa cultivars are genetically very similar and there’s a high probability that a bioactive profile will be about subtle variations in the amount of the chemical compounds within the fruit – so a chemical profile can better identify a unique compound and the amount of it present. Also genetic testing is costly and is simply not feasible on a project that is not currently funded.

The Gas Chromatograph-Mass spectrometer (GCMS) compares the chemical profiles within the cultivar sample to hundreds of thousands of identified compounds within an existing database. They use databases that have many compounds. They’re looking for the differences in the profiles between each cultivar in terms of the types and amounts of each compound.

At the same time, PhD student Mona Mokhtari also profiles the anti-fungal activity of the peel and pulps of each cultivar, to see which varietal has the highest bioactivity. She then uses advanced statistics to guide which chemicals in the GCMS profile seem to correlate the best to the observed differences in feijoa antifungal bioactivity.

In Andrew’s lab, they’re quantifying the anti-fungal activities of the cultivars’ compounds using laboratory strains of yeast. It should be noted that fungi like all microbes, build up a resistance to anti-fungal agents. Science is thus seeking new anti-fungals. Using the laboratory yeast strains, it can be determined if the antifungal activity is being achieved via an already established antifungal pathway or a potentially novel antifungal pathway.

At this stage all 16 cultivars have tested positive with anti-fungal activity.

One cultivar unique to Nigel has been identified as having the most anti- fungal properties. The cultivar is a very edible one, albeit with a very short shelf life. For Nigel, he has a proof of concept – that he can and is producing varieties with certain properties that differentiate them from the standard mainstream cultivars in NZ.

PhD student Mona Mokhtari is working with Andrew and Rob across the School of Biology and the School of Chemistry to undertake her thesis “A functional genomics approach to the mode of action of bioactives derived from feijoa”. Mona carries out all of the lab work for this project.